may be an odd patterned TT, or one of many spiney's. You'll know pretty quick if It's a TT generally they are rather reclusive but will eat most smaller fish excludeing cory's and loaches. and they can get about the same size as a fire eel so will grow relatively quick. mines gained about an inch in less then a month and was about 5-6" when i got him. peacocks and most other spineys tend to grow relatively slower and max out about 12" their diets are all relatively the same though so you shouldn't need worry about it overly much. just be prepard if need be for a larger tank for it or a new home if it is a TT. as for price.. always depends what someone is willing to pay. it's alot harder finding a nicely patterned TT then a broken pattern in my experiance. and the bigger and healtier it is the more $ you can hope to get for it. the petstore i bought mine from doesn't carry fire eels but offered to buy my extra 1 once they reached adult size for what I paid for him. because simply a large fire eel is easy to sell. and the fishstores around ere never give money for fish, ever. It's all demand/availability.
i got the same eel in my tank got it from exoctic aquatics on friday wasnt sure wot it was nither seems pretty livey thou always out and about payed 14.50 4 it where bouts in belfast u from