The bags being sold at Walmart right now are pretty good and the price is right.
I have a Hart rest with a windage top, some home made leather sand bags that I stack, a small Midway rest, and a home made pistol rest. One of the home made bags is a large bunny ear for use under the forearm, and it works very well with just about every rifle.
Good bags can be made from the legs of old jeans by filling them with sand. I have a small one filled with beany baby guts that I can carry out hunting. If it gets wet, the filling won't rot, unlike rice or other old time natural fillers, and it's light enough to carry.
The best inexpensive (and they aren't all that cheap) front rest I know of is the large one with the elevation wheel sold by Midway. They're heavy and have a good footprint. But I wouldn't get too hung up on a mechanical rest if you have good bags and maybe a wood base to set them on.
Don't buy one of those hard plastic rests sold by MTM, they're horrible and cause vertical stringing.
Here's a picture of my leather bags piled up into a front rest: