Look at one of the lower end new iMacs. Soon you will not be able to upgrade that 2007 model to any of the security upgrades as the capabilities of the software won't support it. We upgraded all of ours two years ago, just in time for a burglar to break in and steal several of them. So we upgraded the replacements. . . and the burglar got boat anchors suitable for selling for parts machines as we wiped and locked them remotely.
Correction, it’s a late 2009. I bought the 2007 new, with Applecare, but had a hardware issue so they gave me a new machine. It had 2gb of ram which I upgraded to 8gb to give Sierra some more comfort room when it came out. Still going strong now but with some minor hardware quirks. I’ll be upgrading to a newer model this year.