Totally personal.
Bags in the triple digit range quickly start to lose their appeal for me. As the price goes up past this point, the "features" get relatively smaller, while the price gets higher.
The difference between starter bags to intermediate bags is a large disc capacity for the most part.
The moving on to advanced bags, is increased capacity and side storage, with options for bag straps.
Moving to premium bags typically grants larger side storage and a "bit" more disc capacity.
Moving to backpacks has no increase in capacity, but a better weight distribution.
Moving to top-of-the-line bags gets you a bit more disc capacity, better materials, a bit more side storage, and all the straps, clips, pencil holders, zippers, velcro your heart could desire.
This doesn't exactly hold true in all cases, but seems to be pretty typical. I like to maximize disc capacity with reasonable side storage. I don't plan on carrying enough gear to go camping. Just wallet, keys, phone, towel, pencil, and if cold hoodie, gloves, hat. Most $50-75 bags can cover that. All the other, small features just don't interest me enough to warrant that increased cost.
Playing for 5 years, pretty consistently. About once a week in the winter, and 4-6 times a week in the fall/summer/spring and competing at tourneys. Currently using Innova Competition bag without straps. Even taking my game pretty seriously, I don't see the need to upgrade past this unless I was going to spend WAY more time at tourneys, then I'd probably grab straps and a seat, that's all.