Advice on how to plumb my new tank

So I recently bought a tank from my LFS ,the dimensions are 24"x18"x18" (WxLxH) and its already got one 2 3/8" hole drilled the the top left corner of the back pane. No overflow installed. I want to add a 10g sump to it.

I'm not against drilling another hole into it, but I don't have a hole saw and I don't really want to try drilling it myself. My LFS is charging me $20 per hole, which is a little expensive if you ask me.

Any help will be appreciated.

Thanks.

Use the drilled hole as the drain and hang the return over the top.