I would suggest just getting an electric violin because violin pickups will feedback a lot in noisy environments. Else look for Shadows Nanoflex undersaddle pickups, buy from ebay. But do note your violin will sound vastly different since there is something slotted in under your bridge, and bridge will need to be modified as well to accomodate the pickup.

If you're interested in cheap electric violins I have a heavily upgraded Stagg, with Wittner tailrests and shoulder rests.