My camera cart cost around £150 and folds down to around twice the size of my AC bag (2'x3'x1')
It's based off of a Rock n' roller style cart from Thomann in Germany- The Millenium Go-Cart for around £80.
I added a top shelf with QR plate, dual baby pins, a tripod hook and most recently, an end bag for stands and tripods.
The main benefit of this cart, other than the small size it folds down to, is its ability to not only extend to almost double it's length- but also to lock anywhere inbetween to create a custom length cart.