$100,000 if you are serious for a website. It'd need to be a secure, searchable database that is easily updated.

For every car sold expect 100 page views. Bandwidth (all those pictures and page views) would need to be high.

Security is an issue too.

As for the costs to sell - have a look at thier website for the costs - it's not a big secret.

There's been a lot of attempts at building car selling sites, few survive.

There's probably room for a site that sells used parts. Currently to get parts people have to phone around. I have a Toyota Landcruiser and parts are horrifically priced so I try to get used stuff where I can. Every 4WD owner is in the same position - prices are usually very high.

Landcruiser headlight NEW - $220. USED - $40.

You could focus on 4WDs at first or exotic cars like SAAB or VOLVO for a parts website.

Your only other alternative is to get a financial backer, but given the miserable track record of previous attempts at a used car sales website then I don't think it would be easy to find a backer.

Anyway, as you are still a teen then if you get saving I expect you'll be ready by about 2025 to invest. Of course by then we'll have space ships so maybe you could sell used space ships.

Here's some website name suggestions for you:

www.Spaceships_R_Us.com