Vats are available from 3rd party sources. Some of us are using the MOAI vat with a small modification (do a search for MOAI). 3rd party resins that work without any modifications are available from multiple sources, Myself and several others here are using ApplyLabWorks with good results.
The only issue is repairs and repair parts. Some parts you might be able to find, others are more or less proprietary, and FormLabs is not making any of them available, nor are they repairing these units any longer. So this is the real sticky issue. What happens when something breaks.
For $300, I’d buy it if it’s running order. Yes, DLP printers are making good strides, but what set the Form printers apart from the rest is the software. If you like to tinker with open source software and such, then maybe a DLP should be something you should look at, if not, then there’s no substitute for PreForm.