It's called a loan. You can get a business loan from a bank, or a home equity loan or second mortgage.

In the second case, you're not mortgaging the domain name; you're mortgaging the house. If you default, then the bank will take your house and sell it. The reason you don't mortgage the domain name is that the bank does not want to own or try to sell a domain name. They have even less idea about domain name values than they do about home values.

I've noticed recent startups aren't that fixated on having the domain from the get-go (dropbox is a notable recent one).

I have no idea what stage you're at, but is it worth considering just going with websiteapp.com, getwebsite.com, websitehq.com or whatever until you've proven the concept enough to make the purchase worthwhile?

Domain names don't seem to be very fungible, and it's a market where it seems that professional dealers seem to have an unfair advantage (like real estate). Nightmare.

$75k is pretty pricey for a domain name. Could you use that $75k in some other way to get traffic to the site? I'm assuming that the name you want is something like shoes.com where people are likely to type that directly, but isn't this less of a draw now that we have search engines?

To paraphrase Clinton's winning phrase from his first election, "It's the product, stupid."

Create a great product, provide value, and people will come. Case in point, you come to news.ycombinator.com. Not the best domain name out there, is it?

You can also go the mint.com route and trade a little equity for access to the domain