whats the cheapest domain name register site?

The cheapest domain name registrar would be www.1and1.com at $5.99/year.

Just be forewarned that creating name servers and changing their IP addresses at 1&1 can take up to a week OR LONGER compared to other domain registrars. If the domain name has a lot of importance to it, I would suggest paying a few dollars extra to get it somewhere else.

Is that 1and1 price a special deal, or is that the permanent price? The cheapest reliable registrar I knew of was Namecheap.

That's their regular price.

All things considering, they aren't as bad as... RegisterFly, it's just for some mysterious reason updating name servers and their IP addresses take WAY too long.

whats the cheapest domain name register site?
How many domain names are we talking about here? Does it really matter that much for the difference of $2 - 3 per YEAR?

Bulk registering was one thing I had not considered. If that's what the OP is doing, http://www.nameking.com might be his or her best bet.