the chainset on my mountain bike is very badly rusted. it wasn't particularly good to begin with, and I didn't maintain it at all, really.

I want to replace the whole thing, chain, chain rings, cog set, derailleur, shifter too I guess? but I want to know the least amount of money I should spend, or the best cheap options. also some maintenance tips would be nice, lubricant advice or whatever,

thanks!