FOR SALE: 27" iMac Computer. This is the mid-2010 model with an i7 processor. Among other things, this particular model has Target Disk Mode, which means it can be used as a 27" display for another computer. However, it does not currently have any OS installed, so you will need to get an appropriate version of MacOS from Apple and install it yourself.
I can turn it on to show you that it works but I am not able to provide tech support beyond that point. I *think* it has 12 GB of RAM and a large hard drive, but I'm not sure. Here is a general information page from Apple: https://support.apple.com/kb/SP695?locale=en_US. Keyboard and mouse included.