The only way you'll get a cheap ethernet card for the Amiga is if you buy a 10Base2/AUI card like a
Hydra AmigaNet or a
Commodore A2065
Everyone wants 10BaseT, no-one can be arsed to piss about with different cables, adapters and network cards.
Not as bad as it sounds,
AUI to UTP (RJ45) transceivers are very cheap these days.