I'm thinking of doing computer repairs / building over the summer for some extra cashola. How much more money should I charge, above the cost of components?

well, i would charge $50 dollars an hour (£25)
plus parts then plus a small labour charge, i.e. $20 (£10).
But it really is up to you! ~ think about what u would be willing to pay, and go from there.

Depending on how efficient you are, $20-50 sounds about right. If you venture toward the low end you won't make as much but you'll likely have happier customers (and maybe even return business)

Well, I would charge the customer the whole cost of the components + shipping. Plus I'm only looking to earn around 500$USD to 1000$USD over the summer.

Yeah last summer I setup networks for people and i asked for £25 ($50) for 3 clients and configuring the router etc... and £5 ($10) for each additional client.

so a 4 client network came to £30 ($60) and took me about an hour

All prices are exculding h/w costs of course.

look at the geek squad, then divide by 3

When I did computer repair working for myself, I charged about 35-40 an hour and I had a lot of new customers and returning ones, so that price range should work fine.