http://v4r6k4k35jz3htygpawhyu22hoe2zip3kpwdzogc4g2eup37lpz72yyd.onion/retro
The adapter plugs into the floppy pins, and presents a USB interface to the motherboard. That adapter is under $10 USD.
In fact, I've seen an adapter card that will do the same but for 5.25" floppy disk drives. So, when I have more money, I should be able to have not only a 3.5" FDD, but a 5.25" FDD in my system, running alongside new solid state drives, Blu-Ray disc drives, and of course a few regular hard drives.