Millett makes a good pistol rest that won't break the bank. It has a v-notched front end and an adjustable rear grip support to help with vertical aiming. It gives you very good repeatability.
Outers has a very nice "Pistol Perch" that costs 3 to 4 times what the Millett does, but I haven't tried that one. From the pictures, it looks like it would be easier to adjust.