New to reptiles

Question
So I've been sitting on this for a while to make sure I'm not impulse buying a reptile, however, I still have no clue what type of lizard would be best for me and could use a quick consultation.

Obviously I am a beginner so not looking for anything too troublesome or mischievous.

So far tank wise, I have a 10 gallon (couple year old fish talk) but willing to upgrade to around 20gal (can't fit much bigger in the space).

After initial set-up costs (not too worried about that) I'm looking for something reasonably affordable to maintain. I would hate to find out I took in something that will constantly empty my wallet every week.

So to sum everything up, I'm looking for something reasonably mellow-ish (although I understand I might have to work with that, not a big issue), something where ~20gal should be enough (maybe add a 2nd one at some point down the road?), and something that is generally pretty affordable to care for and maintain in the long run.

(Also, not important AT ALL, but I would prefer something with a more tropical-like habitat as I  generally find a desert set-up kind of an eye sore. But that's all me being picky and I can obviously work with the right animal)

I genuinely appreciate any help and suggestions you can can provide!

Answer
Hello Chris,

A good starter reptile for a 10-20 gallon tank would be either a leopard gecko or a crested gecko.  They both do well in that sized tank.  They are low cost to maintain & wont eat you out of house & home either.
Both species become very tame if worked with & don't mind being handled.  
If your preference is more of a tropical set up or environment I would go with the crested gecko as they live in tropical rainforests.  I think you would enjoy keeping one.  
They do well in the 20 gallon tall tanks, too.  
If you have more questions on them, let me know.

Tracie