The cheapest one ATM is a mares puck at $150. They come with the cheapest uplink cables, too.
Where it gets interesting is if your diving takes you into the grey area between "no stop" dive and mandatory decompression. Mares and Suunto err on the side of deco. Some people just don't go there. Some don't dive with scuba police and when their computer errs on the side of deco they just do the stop and don't tell anybody. Some will tell you that instead the computers that err on the side of "no stop" are the only way to fly. If you don't plan on pushing it in the next few of years, you needn't care. If you think you should care, the ones that err on the side of "no stop" cost $100+ more than the puck: oceanic, sherwood, genesis.