Im not too sure in cost difference but my Line-X is simply amazing! The Line-X wont fade easily I know this because we have it on the back part of our blazer and on the inside. My brother has a rhino and it faded really quick and the cargo tends to slide around a bunch!
Really like the Line-X liner. Had a plastic insert for years and had the Line-X done a couple years ago and kick myself for not having done it originally. No sliding at all. I was especially impressed that even an empty 5 gallon plastic bucket doesn't move.
I have had Rhino in 3 different truck beds and had no issues, except for fading. (Its a truck bed that gets used, fading is the least of my worries) A friend of mine had Line-X in his (only one I know for sure with Line-X) and my FIL has Toff on his. His Line-X was harder and slicker (no noticeable fading - but he didnt use his bed and washed his truck religously so not sure this is a fair comparison), Toff was softer but has held up well, albeit with some fading. Again, FIL uses his truck. Each product should cost roughly the same. If I remember right, Line-X was the highest and Toff was the lowest that I priced, but the prices varied considerably between shops, even ones with the same product.
I suspect that the MAJOR difference in each of these is not necessarily with the product but with the prep and application. I would find a shop that does good work and is convenient to you. Then use what ever product they promote.
One suggestion, if you use the bed of your truck, pay the extra charge and have them spray "over the rails".
I had Rhino in my '99 Z-71 and I wouldn't recommend it. It peeled off on the railing and the fender wells. On top of that after about six months it looked like it had been on there for six years, faded quick.
Steer clear of Tuff. They are located on Hwy 3. They also offer a lifetime warranty. I had one on my last truck. It started flaking off and they said as long as it was under a silver dollar size they could patch it. It looked pretty cheesy. I probably had 40-patches in the back. Everytime I had 5-7 patches I would carry it in. 8-10 trips was waaaaay too execssive.