In need of advice

Question
I got my first mouse in January of this year.  I was lonely but didn't have much money and decided a mouse would be a cost efficient idea.  Dorothy was a great companion but I had been reading about how social mice are and how they need a companion.  So I went to a newly opened pet shop and bought what they told me was a female mouse.  Two months later I find that my newest mouse has dropped a testicle and move quickly to separate him from Dorothy as I do not want babies.  I have a very busy schedule and two mice are plenty for me to care for.  I decided though that I had to at least get a male and female companion for both.  Two weeks ago I bought Kanga a young male mouse.  Introductions with him and Hedge seemed to go well until I heard Kanga squeaking and found Hedge mounting him from behind.  That was very disturbing to me so I separated them.    When I tried them together again later Hedge started biting and pulling on Kanga's skin.  
I've seen some fighting between Dorothy and Hedge before but one or the other always stood up from himself and Kanga wasn't doing any of that so I thought maybe he was too young and decided to put him with Dorothy for a while until he got a little older.  When I put dorothy with Kanga she attacked him viciously and threw her tail around.  Also, that same day I realized to my dismay that she was pregnant.  
I have NOOO idea what to do.  I am pissed at the pet store for putting me in this predicament in the first place.  I am struggling to get a full time job and just don't have the money to keep spending on these mice.  Do you have any suggestions for how to handle this situation?  I am afraid to give away the babies as somebody may use them as snake food so I need to figure out how to keep all of them together and happy in as few cages as possible.

Answer
Hi Brittany,

Oh no, that sounds so frustrating!  I definitely understand, and I'm sorry for you that the pet store did not give you better advice.  :(

The pet store *should* take the mice back, but if you're worried they'll sell them for snake food as well, here's a general setup you can try.  Males almost never get along, so they'll need two separate cages anyways.  I can give you instructions on how to make your own cage in a sec, so you can save a bit of cash.  It's easy, I promise.  :)  That's two cages so far.  I'm not sure I'm following correctly - is Dorothy only attacking the males, or did you try to introduce another female as well?  If she's alone, that's cage #3.  If there's another female she's not getting along with either, I would try my absolute hardest to try and convince them to get along - via several reintroductions and the addition of hiding places in the cage (tissue boxes without the plastic, tp tubes, plant pots or cups, and cheap little woven baskets are all great hiding spots).

We're at 3 cages so far.  When the pups are born, assuming it's a successful birth, you'll have about 4-5 weeks before the males must be pulled out.  The females can stay in with mom assuming the cage has enough space, but you'll need cage #4 for the boys.  They might get along, but if they fight, you'll either need to make more cages or put out ads for finding them new homes.  Most people who are looking for snake food need it to be cheap, so if you ask for a rehoming fee a bit more expensive than the pet store asks for their live mice, then no one is going to pay extra for yours as pets.  Only rehome males one at a time, since ones who are already fighting are likely not going to get along with any other males ever again.

So you have 4 cages right now.  Hopefully, that's all you'll need.  Wire cages can be easy to escape from, *especially* for baby mice, plus they're expensive!  Glass 10 gallon tanks make excellent cages, otherwise here's how you can make a simple and inexpensive cage:

You will need...
- a soldering iron (borrow one if you don't have one), or anything else that gets hot enough to quickly melt plastic (I've heard of someone using a regular iron before!)
- a plastic bucket at least a foot high, with a locking lid.  I get my small ones for 4 USD and my large ones for $6.
- a roll of 1/4 inch spaced chicken wire - this is a couple of bucks at a hardware store
- a glue gun and some glue sticks (borrow if you need to)
- velcro tape and a plastic water bottle (one that fits inside the bucket without touching bedding)

Take your bucket outside and use your heating element of choice to burn out a hole.  My small buckets only need two holes for ventilation, my larger ones need more.  You need the hole to begin above the bedding line and end before the top of the bucket.  Here are two photos, so you can get the idea - http://tinypic.com/m/a58ejd/1  and  http://tinypic.com/m/a58emw/1  Those are photos of my small buckets - perfect for a single boy, too small for a group of girls, or more than one boy.  Also, try not to breathe in the fumes, as burning plastic may or may not be bad for you.  :)

Next, cut out a piece of the wire that fits the hole(s) you made.  Hot glue it on the outside of the bucket.  The hot glue SHOULD hold, but if it doesn't, you can always use zip ties (very, very inexpensive).

Now, attach one strip of velcro tape to back of your water bottle of choice, and the other piece of tape to the inside of the bucket.  Remember to keep it high enough that the sipper won't touch the bedding - or it will leak.  This stuff says it's heavy duty, but if you mess it up, just pull it off and lay down a new piece.  :)  Let it set for a bit before filling the bottle and hanging it, so it doesn't pull off when you don't want it to.

Now you've got a cage, and each one costs about $5-10.  You can make toys and jungle gyms out of hot glued plain popsicle sticks if you're feeling creative, which are also inexpensive, or add a wheel and hideouts made out of nontoxic household items (like tp tubes and the like).  Ta-da!

I know it takes a bit of time to make and it doesn't look quite as fancy as wire cages, but if you're really in a bind these things can be a lifesaver.  I'd talk to the pet shop while your at it and see if they'll at least let you advertise in their store the mice you would like to put up for adoption.  It's honestly the least they can do after giving you poor advice on the mice and incorrectly sexing them.  :\  Craigslist is a good place to try, too, just remember to put a small rehoming fee on there to deter reptile owners.

Best of luck!
-Tam