Here is how I solved the "how to carry my crossbow" conundrum. I have a tactical backpack, I put "d-ring" clips on the molle strap up toward my shoulders. I then purchased a 3 point tactical sling - two points clip to the shoulders. Then, I purchased a d-ring strap that goes around the stock of my xbow. The third point of the sling clips to it. The xbow hangs in front of me, all the weight is on my shoulder and back, I just put my hand on the grip and push a little to keep the xbow away from my legs. I can have it in shooting position (if needed) in just a second. It has worked better than I could ever imagine!
The cost (excluding backpack) - about $20 total. Plus...if you want to save a little money, I made a spare three point sling out of parachute cord and some clips I had laying around the house. That lowers the price to about zero!