

Do you have a single MGN rail on X or two? It’s easy to end up with twist on dual X rails that can be a bugger to try to straighten out.
Also, are you doing a good heat soak before printing, and do your probe results change at all before and after heat soaks?
If you’ve got a beacon on there, it seems like it would be well worth cranking the probe points way up.
If it’s simply bed adhesion, definitely give the dish soap method a try if you haven’t already.
The Litter Robot 3 is a well built and well designed workhorse. I think they cost a little more new than your budget, but they may have a model right around 500.
Depending on your comfort level with the idea and where you live, you can sometimes find them on the used market for a couple hundred dollars, or even occasionally a free non-working unit. Replacement parts are easy to get and install.
They have a WiFi model that can use an app to alert you when the tray is full or something unexpected happens, but it works just fine without the app or internet.