I just did this on my project truck and I'll relay what I found. I used the local farm store (Tractor Supply Company) paint and it was around $30.00/gal. Using the mini roller I used it does leave it pretty rough. If you want to cut and buff( wet sand and buff out), you need to do at LEAST 2 coats. Also be sure to use the hardener or you wait forever for it to dry. The reason I tried it was I didn't want the overspray mess in the shop and this is a work truck anyway. Like you said, cost these days is crazy. I sprayed my show truck with base clear about 9 years ago. At that time, Red from PPG was $640.00/gal JUST for the base.
I brudhed the edges then rolled the open areas. Used NO thinner, just the recommended amount of hardener. It rolls out fairly rough.
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I let it set and dry about 3 weeks before block sanding it. You HAVE to have your primer base right if you want a decent finish. Don't think you can fill in lows with your top coat. After a lot of wet sanding going down to 3000 grit, I buffed it out.
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It's nice but in no way a show finish. Let me be real clear. It's a heck of a lot of work, WAY more than most will want to do. I did it for an experiment so I learned it is possible. You're better off having someone shoot it if you don't want a couple weeks of work. VERY touchy on not sanding through and if you do, you get to start all over.
One interesting thing is on the interior and non outside surfaces, I just used a brush. Same mixture and paint. It laid down a lot smoother and would have taken less work to smooth out than the roller. Roller is way quicker and "may" get a more even coat but I myself will use a high quality brush if I decide to do it on something else.
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This was brushed and the pics make it look worse than it actually is. I've had good luck with tractor paint on past projects. I do keep my stuff inside when not being used so the sun fade issue hasn't been noticed by me. If you have some where to spray it, I would.