invest4.us sounds good, kind of like a domain hack. The number hurts the name, but I think you could get around Low $xx or a bit more. Other name, I'd say reg fee
the number should be considered like "for"...us look at this ebay auction http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=230157963153&ssPageName=STRK:MEWA:IT&ih=013