At $500 for bar, seat pan and seat, I'd probably be working for $3 per hour. Note that the sissy bar required $20 for the tubing. That isn't where the cost is. Chrome, glass fabrication, and getting a viable seat mounting system to work, then getting it upholstered are what cost. I have more than $500 in mine, because of my failed mold experiments.
The bar 45t has on his Duster is real close the right angle, but as he said, a tad too long. Something like that would work. Some pieces of 1/4" PVC foam epoxied to shape, then shaped with a rasp, sanded, then glassed, then machined inside would work, but would still be expensive. I don't like the PVC of any substrate in this design because it bulks up too quickly, and the foam provides almost zero strength, even impregnated with resin.
I'm never into the minibike scene for a profit. Just tossing out there what stuff costs an amature like me.