I have a cheap ebay special bungee single point that I've been using for years. It's not massively thick, isn't well padded and doesn't "seem" to be particularly special but I've run it with my G36 and both my M4s without the slightest issue. I even bought a couple more just in case one broke, they were only £3 each, and the first one hasn't failed yet.
The one thing I would advise if you give cheap and cheerful a try is to pay attention to the clip that attaches to the gun, make sure it's something that at least looks robust.
I do keep looking at more expensive ones from time to time but end up thinking about it too much and never get around to buying anything else.
YMMV of course, I may have struck lucky and got the ultra rare adamantium one.