Welcome. Not sure about the map updates, but I don't think there is a cheap fix.
For winter rims, most 17" rims will fit (5x114 bolt pattern) and 17" tires are much cheaper. Check Craigslist in your area to see if there are any for sale. Read through the stickies in my sig for a lot of basic information that you will want to know to keep your new baby running. There is even a post in the "Have questions about an RX8" thread about some of the "wintertime issues" that you will run into. Froth on the dipstick and the surging engine when its really cold come to mind.
If you have questions read those two stickies then ask away. Post some pics if you can.