You can do the work and save a lot of money. I redid a 3h BP steel trailer a few years ago. I didn't shoot the exterior paint, as I don't have a dust free, indoor space, large enough to hold the trailer.

Mine was badly rusted, so I had it media blasted, inside and out, top and bottom. You can't abrade all the rust by sanding. That added $1k to the cost. I added some improvements and the welding costs were about $250. I also added Lexan windows which I made. This was also about $250.

The paint and misc. material costs were about $1k. I used a single part automotive urethane paint that colour matched our two tone truck's colours. The interior was originally brown which was changed to a creamy white. It made a large difference in reflectivity, and available interior lighting.

I would highly recommend a stand alone HVLP spray outfit. I have three systems and find all give better results than my conversion gun. Instead of running my two stage 60 gal compressor, I turn on a motor that is little different than a powerful vacuum cleaner.

If you don't have one, you will need a good 5" random orbit sander. It works better than the 6" in getting around curves and into tight places. If you use PSA sandpaper, it is about 1/3 cheaper than the cost of hook and loop. Purchase the open gold paper, not the gray stuff found in hardware stores. Ebay is a good source. I use Mirka brand. You will need a lot of sandpaper.

By doing all the prep work, priming, conversion coating, masking, pin striping, painting the interior etc, my total costs were just under $3k. At that time we were planning on keeping the trailer indefinitely, so the costs would have been amortized over many years. We had already owned the trailer for about 13 years.

BOL  Gard

I just repainted my 3 horse trailer w/dr. Prepping is the hardest. My boyfriend does this as a business, doing auto paint, but I had to do the majority of the work. We wet sanded and ran a disc sander over it to make sure the paint would adhere to it. Took a round 2 inch steel brush that hooks into a drill, and went over the rust spots. We used tractor paint and hardener from Tractor Supply. Cars take about 3 coats of paint. The tractor paint took 1 coat on the trailer. I bought 3 gallons and we only used one and a half. We later had to touch up one panel and used a mini roller on it. You can't tell we touched it up with a roller. It blended so well. The label even says you can use a roller. We undercoated the fender wells and seam sealed the roof joints. The preparation is the longest, most tedious task. According to the paint label, you don't have to do all the prep work but we did as I wanted it done right. I now have what looks to be a brand new trailer and it only cost me about 300.00 total in supplies.

 ETA: Boyfriend and a colleague of his both quoted me around 3000.00 to have it done by someone else.