How many parts are we talking? I sounds to me like you are the perfect candidate for send-cut-send or one of the many many other services that take your CAD and build parts. You get to choose from materials your printer couldn't do (not matter what you have something cannot be done)
Low volume stuff, single digits of parts, unless I find that niche, and i might outsource then. I'll keep the send-cut-send type stuff in mind. There are variations to certain parts that I'd like to iterate on, for example, intake runner lengths, diameters and shapes, various adapters/converters, panels/covers, etc. Plus, it's fun to do things yourself and learn along the way. It's not just about the end result.
Using a service would be better for a final part in a better material for the sake of longevity, not just 3d printed either, but cnc'd aluminum for example. Plastics can only go so far, but for short durations in some stressful situations, like intake manifolds, they can give you information. Having a printer in house will let me prototype to verify functionality of some engine parts, and being able to print in resistant materials will let me make final parts of less stressed parts in areas exposed to fuels, oils, etc.
When you have a printer, cycle times can be much shorter…and a few fast cycles with a job shop will pay for a printer.
Small jobs from small customers are not a high priority for job shops. Neither are cheap jobs.
Having a printer means you are able to work on projects at 2am Sunday.
those are the tradeoffs. It sounds to me like 3d priting isn't even a good fit for what the guy wants to do.