An ASN isn't needed unless you are multi-homed. If you're connecting through just one ISP, you can do BGP peering with them using a private ASN. That said, if you do need an ASN, I don't know why they should be so expensive.
Yes, I understand. I set up my first AS in the 90's, back when you were considered a god if you had a T1 line. We had two T1's, one to MCI and another to BBN!
