what is the best shooting rest out there:

-that's not expensive, as it will only be used to zero rifles
-need one that can hold the rifle in a fixed position (to help me zero faster, minimize shooter error)
-flexible on different rifle stocks available, to fit standard stocks to fat stocks

i've looked at the shooting bags (which cost 20-30 bucks), if i have to spend 20-30 bucks, might as well spend the 50-70 on a shooting rest.
people recommend sand bags for shooting, but i will be using this for steadying the rifle not everyday shooting.

-0-

or if you have other ideas for holding the rifle in one position, i'm all eyes.

cut the legs off old pair of pants get plastic bags put sand in plastic bags put  plastic bags in pants legs staple shut... boom homemade shooting bag.. They work great for me

I would shy away from zeroing with a rest or bags other than your initial zero, if that.

The POI is going to change depending on what position you're shooting from. Whatever position your major use will be is the position for at least final zeroing. Prone is actually a good position to zero, since it has some aspects of position / pressure / recoil impulse from most positions, sort of a middle ground, and it is more stable.

For working up loads, or shooting factory ammo to find the rifle / ammo mechanical accuracy potential, a good rest, rest / sandbag combo, or sandbag setup where you eliminate the shooter as much as possible is desired.

I don't have any suggestions on which way to go, brands , bag or rest size etc, as I am looking myself. I traded a car years ago that I forgot to get stuff out of, and my good bags was one thing. I was pressed for time, dad had just been sent to a hospital 35 miles south of the dealership, and I had to get my son back to his mother's by 7pm which was 55  miles north of it, and had about 7 guns and other things to get out and make two trips to my home and back and it was almost 5pm( was trading a Crown Vic on a Neon ).

Anyway, listening in for suggestions.

of course, i'd like to use sandbags, any tips on how to stabilize the rifle (keeping it from tilting left or right) like a rest would?

basically, i wanted to try the 1-2 shot zero.  shoot one, adjust W and E to match POI.

I got tired of burning holes in my sand bags and making a mess.

I bought a Range Systems Sight Block. http://www.inrangesupplies.com/index.php/dura-bloc-688.html

It is heavy but very stable.

You can flip it around to shoot different heights, and even using it with a revolver it hasn't sustained any noticeable damage.  

I sewed mine and they work for me too.

I also have a Caldwell Lead Sled Solo designed for AR rifles to use with a 30 rd mag. Cost is under 100 bucks.

Zero in position.  Use rest to zero and you're zero will likely be slightly off when shooting from your shoulder.

Deleted duplicate.

Free float rails eliminate most, if not all, POI shift from shooting position, support hand placement and bag or rest variations.  For bags, I use leather shooting bags filled with ordinary sand. Front bag is the owl ear type in an adjustable rest, rear bag is deep V rabbit ear style used to stabilize and hold the rifle and to squeeze for fine tuning the cross hairs with the support hand.  Precise, predictable,  repeatable, relatively inexpensive.  Really, you can use anything that can hold sand, and shape as you need.

With a free flost rail and sighted in this way my prone groups using a true shooting sling or even shot off of a rolled up blanket on the hood of a vehicle with no other support are showing no significant POI shift.

I use a lead-sled, similar to this www.amazon.com/Caldwell-Lead-Recoil-Reducing-Rifle/dp/B0023MHZLA , although I paid much less years ago.

I use it only to test which round provides the best precision for a particular rifle.  Zeroing is performed in prone position with a bi-pod, to simulate shooting in the field.