The smallest FPGA
https://www.digikey.com/en/products/detail/microchip-technology/VERYVERILOG/29020656: $13.31 for a tiny, tiny programmable logic chip.
https://www.digikey.com/en/products/base-product/microchip-technology/150/PIC16F13145/733403: The raw chips for the above, cost a dollar or two.
DSP
Learning
BYU computing Boot Camp: Better than nothing, but still has holes.
The Art of FPGA Design: Specifically about delay blocks, but has other useful tidbits.
FPGA Design Process: Also has a bunch of other useful tutorials, but is beyond intro level.
Mandelbrot lab: Base site also has useful stuff
Quartus examples: From Cornell ECE5760
Altera Cookbook:Also from Cornell
PYNQ
Official Site: Very broken
Github Tutorial: Also a bit broken.
PYNQ-Z2 Has info and links to resources. Somewhat broken.