Well, it's just my opinion but I daresay most people who want a drop-in pickup that adds clarity without costing a fortune get a Dimarzio Model 1. It's one of the more popular SG pup replacements and costs under $100.
Actually though, there's nothing wrong with the stock pickups. You just have to EQ your amp differently than you would for a Fender bass. Boosting the mids and cutting the bass is key, IMHO, and sounds especially good to me through an Acoustic B200H head with a 1x15 cab.
I'd try different strings and EQ settings before leaping off into mod territory. D'addario black tapewounds give the stock SG bass a particularly nice clean tone.