Last two bits I bought came from ebay and they were maybe $20 landed (ie., including shipping). As stated mops.ca and bulkreefsupply.com also sell them as well.
For schedule-40 bulkheads, ie., the black ones the holes sizes would be
1" bulkhead - 1-3/4" hole (45mm) -
http://cgi.ebay.ca/45mm-Diamond-tipp...item1c0f8dfe4c
1.5" bulkhead - 2-3/8" hole (65mm) -
http://cgi.ebay.ca/65mm-Diamond-tipp...item518fdcd3e9
If you go schedule-80 bulkheads (they grey ones) the hole sizes will need to be bigger because the wall thickness is larger. You don't need schedule-80 in our hobby but some people like grey better as if they are looking at the pipes instead of what's IN the tanks but hey, whatever floats your boat.
I have bought from the seller I linked to. Would highly recommend. Yeah the bits end up coming from Hong Kong but you'll have your bit within 4-5 days, at least I did (I bought from them twice).