Alternatives to alkyd for lower-end paint jobs

I have been looking around for a cost effective alternative to short-lived alkyd tractor paint, for quick-and-dirty tractor and implement paint jobs, and trying to figure out whether the urethane-modified alkyds are worth the extra $. This is not easy, because while there are industry-standard tests for durability many paint manufacturers just won't share the results.
I just stumbled on some interesting test results from Coronado which allow direct comparison. Coronado (which is now owned by B Moore) doesn't make any tractor or auto paints, but makes a full range of medium and heavy duty industrial paints that should serve the purpose equally well, most of which are available in custom colors. The results are interesting - the accelerated weathering result is probably the most significant for tractors and implements which will live outdoors.

Plain alkyd
Accelerated Weathering - 500 hr. (higher is better) - 65%
Abrasion (lower is better) - 140 mg
Salt Fog - Rating 9 0.04%

Urethane-modified alkyd
Accelerated Weathering - 500 hr. (higher is better) - 70%
Abrasion (lower is better) - 120 mg
Salt Fog - Rating 10 0.01%

2-Part "real" aliphatic urethane
Accelerated Weathering - 500 hr. (higher is better) - 95%
Abrasion (lower is better) - 44 mg
Salt Fog - Rating 10 0.01%

I'm not sure exactly what each number means but you get the idea - urethane-modified alkyd is a fairly small step up from alkyd, but real 2-part urethane is a huge one. The results for urethane-modified alkyd should be very similar to what one would get from an alkyd with the hardener.

I've found the Coronado 2-part on the net for about $65 a gallon custom mixed, not much more than most urethane-modified alkyds, which means it should be possible to paint a tractor using the two part for only $50 or so more than using "tractor paint" alkyd

Well , Kyle , I just retired from a large company as paint dept foreman and we bought our paint in 55 gal drums and catylist in 5 gal cans many at a time. Naturally we got a better price than the occasional user. We paid $45 per gal of sprayable product in true acrylic urethane orange. Our special colors were $75 and our 2k urethane primer was $40. I don't know where you are located but the company is Niles Coatings in Niles MI. They make their paint from scratch and have their own lab for testing etc. The urethane we got from them was hard enough after 24 hrs to be walked on without problems. The size machines we built required walking on to finish assembly and hosing etc. I will give you the name of the sales rep ( used to work in engineering) and his cell #. Can't tell you what type deal they can give you. Explain to him exactly what you need and let him give you their options and prices. Please don't quote any of the factory prices I have used for reference as they will not apply to you but I believe he may be able to hit your price and usage range. His name is Brian (Duke) Lawton and 574-315-9981 and tell him Randy from (Morbark) referred you. I have been an avid PPG user and prefer base cote clear but for implements it is just plain overkill so I had him mix/match up some JD green and used it on my mounted cultivators for my "B". This is hard shiney stuff. At work we had to mask and plug every thing with exposed threads or tapped holes because after a couple days the assemblers couldn't get the nut on or bolts into the holes , the larger ones even with impact wrenches! I will definately use it on ALL implements / wagon gears etc from now on. Again, the price will be higher on small lots but check him out. They will drop ship paint too but don't know the details. RB