For a very generic idea on price, online a .40 size glow engine often sells for around $40 and a .60 goes for closer to $60. Obviously higher quality, rare, "in-demand" engines cost more and garbage costs less. At swap meets you may find much better prices. Heck, it's not uncommon to see a .40 size trainer with engine, servos, and old-school receiver for under $100. The snag is that many of these old engines haven't been run in years (decades?) and are often very gummed up and in need of a full rebuild. It's not difficult to do, just something to be aware of and watch for. A little time cleaning and oiling puts it back into working order.