Hey I get it, I've definitely plumbed the exhaust on more than a couple vehicles with leftover pipes, generic parts and a few extra connectors and elbows.
But that's mostly because I can do the work myself. And honestly some of the stuff I did in the past I wouldn't do again, I'd just buy the right kit to begin with. If it can be done for $200 or less I don't think it's a bad plan at all. Just realize that at some point it's probably more cost effective to just buy the right kit!