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MTC Radio has the Uniden BC-SGPS Universal GPS Kit for $48.95 and the Uniden A28100B Nylon Carry Case for the SDS100 for $16.49 at checkout.
Spend $100 and get free shipping and use coupon code "nicehat" for even more off.

You can certainly assemble your own GPS, but this is the cheapest I have ever seen it go for.