The ex-Alibaba KU3P boards are available for under $200, although you do need a separate JTAG cable with flying leads to load designs on them. I recommend starting with that. I'm building the next-generation version of Corundum on those boards, at least initially. I will certainly be adding support for Alveos and such in the near future. As far as adding functionality, it depends on what you want to do, but in general you should expect to have to do a fair amount of tinkering with the design.