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Some poeple have been ordering the ACA 500 card from AmigaKit.com. Its about $100 but it allows you to have a compact flash card hooked up to your Amiga, and it comes with extra memory and Kickstart 3.1. Probably your best bet for the money at this time.
I use the ACA 500 and I recommend it, however, unless you have a Rev 6A board, I'm not sure I would buy it.
I have several Rev 5 500's and I couldn't get it to work with them, in spite of the web page that says it does work with Rev 5. After I obtained a Rev 6A 500, then it worked great! I can recommend an HxC floppy emulator from lotharek.pl as well. You can either buy a slim version and install it into the 500 or use the cased external version.