Ken,

I had a similar problem a few years ago where the boat I bought(used) had a rotten trailer. I too looked around with limited success and finally built my open with a friend who was a welder. We kept it simple, used good materials and had it built in a weekend. It was solid and after a few trips to the junkyard getting odds and ends I had a good looking, clean trailer built to my specs. for about $300.
Of course, you need to have welder friend!

If that's not an option, look at junkyards, used boat dealerships or classifieds for "utilty" trailers. The advantage you have is that driftboats are flat-bottomed horizontally so your trailer basically needs just a flat pad of some kind with small bumpers on the side to hold the boat in place. I've seen all manner of trailers carrying driftboats and many are not actual "driftboat trailers" They are fairly easy to convert with the addition of a good quality winch and a roller on the back lip so the boat can roll smoothly on and off of the trailer.

Good luck.