OP, even after your second post it didn't become clear what exactly you're planning to do. OK, your Mac is too old to instal Bitcoincore and run a node. But why exactly you need it. Why lightweight wallets like Electrum isn't an option for you, I'm sure that it would work on your Mac. Yeah, you won't be able to run a node on it, but do you really need it?
And as said above, why exactly you need Mac? PC's with Windows OS is significantly cheaper. And you can buy decent used PC for much less than $800.
And finally, you haven't explained clear enough what you're planning to do next. Because now you just come to forum asking money from random strangers, do you expect that money comes so easy. After all, Bitcointalk isn't crowdfunding platform.