I have just recently traveled to mongolia from the states.
I flew with Korean Air the ticket was at the time was 1500.00 as opposed to China Air's 1300.00. I read some reviews on China air and decided It might be worth it to spend a little more for a more comfortable 13 hours besides I wouldnt need a Visa. I was shocked at how great the service was we had two meals as much wine as I could order and they were very polite. I think that I spent more money here but it was totally worth it.
I also had to change my money. Well they took a chunk of cash in the exchange well that was to be expected. Then at the air port I thought they would take a chunk as they did. However they did not thave enough money at the airport to change my Tugrik. So I left the country with almost $700.00 USD expencting to change it in Korea. No dice. The currency is not traded internationally. So make sure you spend it all there.
Alas I have Around 5000.00 Turgriks. That any one who wants to can buy I'll give you better rate than its changed at my number is 562 787 4686.
I understand I didnt talk much about spending in the country. Thats because you can bargin anything down. Also the prices vary so widely.