As a USPSA & SASS competitor,, I've seen all kinds of range bags, packs, & wheeled carts. Including a lot of folks shooting 3-Gun or using a cart with a PCC in USPSA.
Buying one built specifically for shooting can be pricey.
What I've seen,, and is quite a bit less expensive AND easily made to fit an individual's needs is the simple 3 wheeled baby cart. The center area can carry a normal bag or bags of various sizes & shapes,, while the sides can easily have velcro strapping & a padded base for long guns. What's more,, you can easily use a lot of what you already have to make it your own personal preferences in how or what you normally carry.
And,, if you make it where the bags & such are not permanently attached,, they also fold up to fit in many small spaces. They are easy to push over all kinds of terrain, balance well, and make carrying stuff much easier.
Lastly,, you can often find deals in thrift stores on good used ones.
I have a custom built cart for SASS,, and yet,, I stopped shooting SASS long ago. I built it & it still cost me a fair amount for the materials,, plus my time. Next,, I also have one of those folding, expanding pull carts,, with the cloth storage section. It folds up nicely,, carries a lot of stuff,, (but not long guns easily,) and is a bit harder to drag behind me. But a 3 wheeled baby buggy type balances better, and can easily be made to hold 2-4 long guns,, as well as plenty of stuff.