Depending on the type of bike, $400 for a running bike could be a pretty solid deal.
I'd hold off on spending anywhere near $1k for a first bike. Get something cheap and solid. Get a feel for riding and working on bikes. Then you'll know what you like/don't like and what you want in a bike. You can then spend money shaping the bike you bought with upgrades or by buying a different type altogether.
Don't spend $1k on a stranger's project, you don't know what you're getting. (edited)