LF start up stuff and advice

[Westkes]

I'm afraid we've fallen down the rabbithole of saltwater. We homeschool (radical, I know) and our 9 year old has been researching setting up a sw tank. I have either a 70 or a 44 (octagon) that he could use. Everything runs on aquaclears.
So I'm looking for live rock, or dry rock, a powerhead, lighting. We have enough salt mix for 50 gallons. Would like to get a tank cycling and still have some $ for fish. Please message me if you have anything you think he could use. We can spend a bit but not a lot (homeschooling pretty much equals single income household).
Thanks for reading. I've been lurking in the site trying to catch up with this kid on knowledge and you've all been very helpful with all your posts.