Hi,
how much you would pay for the existing domain name ??
My neighbor proposed me to buy his existing domain
http://hosting.usa-u.com
for 80 dollars.
Domain could be found in Search Engines - so i don't need to advertize it.
What are your suggestions?

Is he selling you usa-u.com or is he selling hosting.usa-u.com??

only subdomain

I really don't like domain names that aren't one word.

Saying something like "hosting dot usa dash u that's the letter u not the word you dot com" isn't that catchy. Even if they get the domain name right, they will probably go to www first.

only subdomain

Its better you register a new domain yourself and then add as many subdomain possible...

I wont even pay a cent for this..

You can't "transfer" ownership of a subdomain, so you would only be buying the use of that, and it would only be available for as long as the main domain was registered and he was pointing to it.

Get your own domain, you'd be far better off, and would only have to pay whatever reg fee the registrar charges (typically < $10).