It's relatively easy to convert a saiga. I use surefire mags with mine which run 20-50 depending on round count and if they are on sale. If you use after market mags for the saiga, you won't need a bullet guide.
You can pick up a .223 for 349+tics, transfer and shipping+about $150 to convert in the least expensive manner. You will need a trigger group, various screws, shepards crook, grip, grip nut and screw, stock, a few drill bits and some black spray paint.
This will get you the base conversion. After that you can take it to a gunsmith for the harder stuff. I've never done anything more than the base conversions and have always been pleased. Dinzag offers many of the harder items to convert, as rather easy but expensive bolt ons.