The cheapest so far 2 point sling are the USGI silent black nylon with two black metal buckles, very basic but durable.
The next one are the adjustable USGI slings used on M1 Garands and M-14 rifles, they have an adjustable buckle, usually cotton or nylon webbing, I prefer the nylon webbing, different colors available. I use this on my M-16A2/ A4 rifle clone.
I also have a Magpul MS1 basic sling at an affordable price and it it quick adjustable, I could also upgrade it with different Magpul attachment points later on.
The Blue Force Gear Vickers model have a basic model that have a lower price than their more loaded models, when you add heavy duty push button quick detachable sling swivels and other quick release adapters, then the price goes up.
I have a padded LaRue Tactical two point sling made for them exclusively by Viking Tactics, it have a thinner, softer webbing than the Vickers, I use it for my heavy barrels carbines.
There are two design types of quick adjustable 2 point slings, there is one that the tail end gets longer and hangs out longer as you tighten the sling.
The other type have no tail that gets longer when you tighten the sling to your body, the tail is kept inside of the sling.