Buying the tools and learning to do the work yourself makes sense if you will use them in the future, either on this truck or future projects.
If this is the only project you see for these skills and tools, farm it out.
If you are going to be welding mostly sheet metal get a GMAW (mig)
with shielding gas. Here is an excellent Article on GMAW (MIG) vs FCAW (Flux Core):
GMAW vs FCAW-S Process Comparison My 2 cents, FWIW
