Cheap, niche option
I traditionally only carry 10-12 discs, so I've never needed anything but a small bag. But I moved to a place that is much warmer and more humid than I'm used to. And I have 2 small boys that like to tag along. So it was always a challenge to carry all the drinks and snacks we all need for a warm round.
I found this at Walmart for $20 on clearance. They sell for $30 normally. I didn't have to do any modifications to the bag or cart itself, which makes it easy to still use it for its intended purpose of packing for a long day at the park, beach, or zoo.
The wheels are some kind of rubber. Not very heavy duty, but a decent size. The frame isn't exactly space-shuttle grade, either. But it's light and as long as the course isn't on a mountainside, it suffices.
I did build a simple box frame from PVC for two reasons. The first is to raise the discs up, since the bag is just one deep opening. (But not as deep as it looks in the pictures. Angles.) The second is to create a sort-of cooler compartment I can access just by moving a few discs. The inside is insulated.
I can fit 18 in the main compartment (mix of drivers, mids, and putters) and 3 putters in the front pouch. The one side can hold an umbrella or stool, and I put my retriever in there. The other side is just a basic mesh pouch you can throw a couple extra bottles, or a birdie bag, mini, whatever.
There are two other zipper pouches. One in the top flap that I just rest against the back of the inside. And one on the back panel.
To make it work as a disc golf cart, I just clip on a bunch of accessories I have lying around. Nalgene coozy, towch, extra towel, maxpedition pouch for my pencils/scorecard/etc.
It's definitely not for hardcore golfers. But for a dad on a budget, it more than handles my needs.