A VERY nice option is a snapbow. about $30, 100+ foot ranges, lasts forever. Link-http://nerfhaven.com/forums/index.php?showtopic=20296
However, if you only want to mod, buzz bee is usually great, the 4b, which can be expensive, nets huge ranges is a nice option or, you could spend less money and get a panther or a range master.
Really, whatever you want/think is in your skill and ability level. Search around, there are some great resources out there. the best part about this is if you don't like what you did to it, get a new one and try again. Buzz Bee blasters are rather inexpensive.
You could always make it into an SVT4B.(replacing the pump and putting it in the front of the blaster and minimizing it) Link: http://nerfhaven.com...showtopic=20524