well first off where did you get this Schwinn of yours? If at a dept store then the answer is NO. If you got it at a bike shop then the answer is Maybe. First of all the minimum cost to outfit any bike that is capable with disc brakes requires two things, First: the frame and fork must be Disc brake ready with either 52mm or 74mm eyelets for the brake to fit on. Second : the rear wheel needs to accept a 6 bolt rotor or a centerlock rotor. Now cost, minimum cost if you need a rear wheel to accomodate the rotor and the brakes (well assume low end mechanical hayes tektro brakes) and levers and the know how to assemble all this (which will certainly cost you more if you dont know how to) $350. Did your bike cost less than this? If so then it is NOT worth it! If it cost more then you need to learn how to bike shop because you could have gotten a bike for that amount with disc brakes already on it! Now lets assume that you need a fork that is disc ready, cost for this at a minimum: $90 for a Rock Shocks Dart 2 at a bare minimum now you total cost could be well over $400, is it worth it yet?
Sure you could do all this for cheaper but not much, depending on how cheap you go on that wheel....
Vince V ever wonder why you have no best answers yet? Keep it up and youll be on a roll to nowhere!