Another way to go about this is to look for a Boyds stock that you think you'd like, and then see what actions it is made for. Then search for used actions of that type. Keep in mind all blind mag actions S/f flat back, c/f round back, c/f flat back, short or long are pretty much of the same quality and price. You might find someone willing to sell you one real cheap, but that does not change the actual/practical value. The other consideration is the trigger. If it comes with an Accutrigger, it is usually considered to be worth $75-100 more than one with an old style trigger. I usually buy older, pre-accutrigger actions b/c I prefer aftermarket triggers and they generally cost about $100. So... take that into consideration...

Action with accutrigger, no bottom metal: $300
Action without Accutrigger, no bottom metal: $200.
Bottom metal and accessories(trigger guard, mag, mag frame, etc.) will affect the value differently.

Again, find a stock that suits you, then look for an actin that will fit the stock. Don't worry about s/f or c/f as long as it matches what the stock is designed for.

I hope that helps.