I think there are going to be a couple issues at play here. Precons are a bit on the weaker side, so your deck may be lacking in draw, protection, ramp, whatever. What doesnt help is Prosper is kind of a strong commander on his own, he does draw a decent amount of removal by himself.
I do feel cautious recommending it, but building your own deck may help out. Knowing your own deck intimately is a better experience than a precon or borrowing a deck, plus you can customize your deck to do a thing you want it to do
Theres going to be no solution to the price tag, which i get. However MTG is a game of rules, and all rules are made to be broken. Yuriko and Derevi get around commander tax, so that you may still build a deck that revolves around your commander.
Technically not dead is up to you to decide whether to scoop or not.