I agree - my experience of that was being given a horrible old computer, upgrading it, and then subsequently building an all new one.  I'm a fan of that approach, and so I'll likely emulate here.  Get a 3D printer, use it, print additional parts, acquire additional parts, build a better one, sell the original.

Price would determine which of those 3 options - I'd prefer a fully functional assembled printer, but based on price would probably compromise and go for a complete parts kit with instructions.