There are a few niches where FPGA make sense, but for things like DSP they naturally parallelize ops well.
The LCMXO3D-9400HC-B-EVN demo board from Lattice can still be found for $60, and Verilog is the most common dialect to learn.
If you are from the sequential CPU/MCU world, than expect to see some very different paradigms. The language define a logic circuit where states propagate in parallel (within physical limits)... latch-up avoidance and clock domain crossing must be handled properly.
If you are good with hardware, there is also the $20 EBAZ4205 (Xilinx ZYNQ 7Z010 fpga has a cpu that runs 32bit linux) since the crash of various crypto currency trends.
T[p: the next generation of Desktop CPUs are supposed to include configurable logic similar to current ZYNQ chips. We shall see what this means when the other boot drops... Good luck... =)