I'm not so sure you'll get anything new - I was offered a decent amount by one of the vendors (not mobiles) for my Nokia 6230, 'cos apparently you don't get much discount on the price of a phone when you sign a contract over there, maybe 50 Lev.
I had no problem in buying a mobile phone but would advise to stay with the pay as you got got a good siemens camera phone in varna for £40 and put 75 lev on it and lasted me a good 3 weeks. But there is lots and lots of mobile phone shops everywhere you go and get the choice of payg or contract.