Got money to spend, but on what?

[my67c20]

Getting ready to do some extensive rust repair work, and was wondering what tool could i receive the most benefit from. I am trying to stick to a $300 budget. I already have a many standard mechanics tools, mig welder, air tools, compressor, hammer /dolly set, hand tools, bench vice, and access to a torch set. Of course this tool does not need to be limited to something for rust repair. My skills set has 20+ years of experience, but are not mastered to a specific discipline. I am working out of a 2 car garage, and 1 bay is consumed with my daily driver, which goes outside when i want to play. So the question is what should i buy? Thanks for all the responses.