Look up your state code. It's on-line, probably at georgia.guv.
What are you looking for? Searching through car trailers on ebay I think you could do a
lot better than $2,700 for an 18'.
Building one of any size is a chore. I bought a big hay trailer made from a mobile home frame several years ago. It was almost untowable. The axles weren't lined up, the frame wasn't square, the axles were too close to the center and it was way out of balance--no tongue weight and the long portion after the rear axles swept from side to side like a stegosaruas tail. It took days to cut that thing apart and weld it back together square--and lots of calculating where to put the axles for the proper balance. I put $500 in steel into it, had to add a set of brakes because all axles require brakes in Indiana--and it was mobile home axles so there are no flanges on the tubes for them. The lights were also poorly installed--and not DOT. I put at least $1,000 into it just getting it usable. It had no tie-down points on it, the deck wasn't suitable for wheeled vehicles. Basically I bought a pair of 30' long 10" i-beams, wheels and tires and made a trailer out of it.
Point is, you'll spend a lot making an 18' trailer--time, effort, money. And it requires tons of thinking before you even start. Don't ever start a big project without putting the thinking into it. No way you could come close to the price of buying one unless you have a bunch of scrap available. It's fun to drive off with a load of new steel, but it isn't cheap. Axles, hanger kits, wheels, tires, brakes, coupler, decking, d-rings, paint, lights, ramps, 1,000# of steel if you are wood decking it and 1,800# if it is getting a steel deck. That's a dollar a pound maybe, or close to it. You can estimate
HERE. Where I go it works out to be a good bit cheaper so I'm always happy with my estimates from that site.
As a rule, I only build things I can't readily buy. That rule keeps me busy enough.