You don't actually need a "chain checker" to check the chain yourself. Here are a couple of easy ways:
Take an ordinary ruler, 12 inches long, and put the mark by the 1 in the center of a pin on the chain. Stretch the chain tight and look at the mark by the 12. It should be near the center of the pin on a link. If the pin is more than 1/8 inch past the mark, the chain is worn out (we say it's "stretched," but it doesn't actually stretch. The parts just wear a little).
Or put the chain on the big ring with the cranks vertical, one at 12 o'clock and one at 6. Pinch the chain at 3 o'clock and pull it away from the ring. If it pulls far enough to expose all or nearly all of one chainring tooth, replace it.
As for your original question, I don't keep track of chain life, but I'm sure I get at least 2500-3000 miles on one, and probably quite a bit more. I've had my singlespeed for 10 years (five as a geared bike, five as an SS) and it's still on the original chain.