Take a look here. Some very good bargin machines.

https://www.dvwarehouse.com/Apple-iMac-Intel-Base-c-5203.html

I have purchased many of my MacBookPros here. I would recommend any 2011-2012 vintage machines. Anything of a newer vintage you start running into problems with right to service issues with the newer machines. Apple makes newer machines unrepairable. 2012 vintage machines is the cutoff for installing and running Mac OS Mojave and Catalina. If you want a cheaper older machine I don't think you would have any trouble running MainStage.
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Musician's Theory of Relativity: E=Fb