Digikey will sell you single Lattice ICE40UL1K FPGA for US$2.75 plus shipping and handling. [1]
These days, a lot of the things that used to be done by FPGAs are now in the realm of capabilities of the Raspberry Pi Pico, and the US$1.00 RP2040 chip it's based on. [2]
Most recently I've played around with the Polarfire FPGAs from Microsemi^H^H^H^Hchip, and previously with the Xilinx Kintex series on the KC705 eval board. The SERDES interface on the Polarfire is way easier to deal with than the monstrousity of a SERDES interface that Xilinx provides (oh the absolute horror that is caused by trying to get the clock signals from the right pin through the right series of blocks to the SERDES). My interest has been in playing around with 10Gbps ethernet and protocols like 10G EPON. Learning VHDL / Verilog isn't too hard coming from C, and there are a number of open source simulators available that work quite well. Plus, it's rather nice to not have an operating system inbetween me and the hardware! The downside is that there is so much to learn: figuring out how to cross clock domains and implement FIFOs between blocks.... I should really play around with the high level synthesis tools that can synthesize C / C++ code directly to hardware. So much to play with, too little time.
These days, a lot of the things that used to be done by FPGAs are now in the realm of capabilities of the Raspberry Pi Pico, and the US$1.00 RP2040 chip it's based on. [2]
1 - https://www.digikey.com/en/products/detail/lattice-semicondu...
2 - https://www.digikey.com/en/products/detail/raspberry-pi/SC09...