Black lab - scratching/biting

Question
My 12 year old black lab has developed what appears to be a nerve problem - if I rub or fondle his underside or other areas his legs start to twitch - he also has started licking/biting areas of his body - I looked but cannot see any infection or other annoyance - can it be a nerve problem or something else?
I have spoken to a vet who obviously states " bring him in " but unfortunately being an OAP I cannot at present financially afford large vets bills
Any suggestions?

Answer
I am not sure that rubs that produce twitches would be anything to worry about.  My dogs all have spots that cause they to kick or twitch...they are like ticklish spots.  

But that said, if a 12 year old dog is acting differently than it has, a visit to the vet is well worth it.  Seniors need more visits than younger dogs.  

You might want to see what it would cost to do the minimum...a vet visit and maybe some blood tests to see if body functions are OK.  If all that works out successfully, you can see if you can reproduce the twitches but you don't necessarily have to go in for all the tests.