I agree with Amy. I also like an apron that wraps all the way around you. Otherwise your coat makes "duck tails" out your backside.
I initially made aprons out of polyester gabardine, and they were nice that they didn't wrinkle even when you threw them around the trailer after your class, but that really isn't a very traditional fabric. It was fine for open shows and "lower level" ADS, but we have moved up in the ranks. So last year I made ones out of a lightweight wool blend which I also found on sale. They have a flat waistband and heavy duty velcro for a closure. Make sure you get the closure close enough to the end of the fabric so you don't get "flopping" of the end.
Make sure that you measure when you are sitting, as your apron will "rise" when you sit. Although some people like aprons to come to the crease of your shoe, mine don't because I wanted to be able to walk around if necessary without tripping over the apron (with my luck!
), so mine come to the crease when I am standing. John Greenall says he likes a long apron, but his wife likes it to come more to mid-calf. If in doubt, go longer instead of shorter. Also, figure where your apron will lay in your vehicle. Are your legs straight down, or more in front of you based on the design of the basket? If you want a long apron, you can throw the apron over your arm to walk around. Also, if you make it long enough, you might be able to get away with wearing shorts under your apron if it is hot and you don't show any skin!
Otherwise, I really don't know of a place that you can get an apron for less than what you want to pay. It's just like carriages, it's not the parts that cost so much, but the time involved.
Myrna