Affordable GPS with maps? I have my eye on the Garmin 800. It looks fantastic, but alas I can't afford it right now. 
I would like a gps / cycle computer that would work well in Europe with maps. 

What are my options? I want something I can couple with wheel sensors for speed (better accuracy). 

Next month I intend to cycle through Czech Republic and Slovakia. 

Thanks in advance
One option would be to use an iPhone. If you use software such as MapMyRide you can integrate it with ANT+ sensors to measure speed, cadence and even heart rate. These sites also have excellent mapping, training review and history functions.

Pros:


You can use your existing phone rather than needing separate hardware
The online version of mapping software allows you to plan routes and review your history


Cons:


Waterproofing the iPhone will be harder than with dedicated hardware, although I have seen solutions (such as Biologic's case) that claim to do this. 
Battery life will be an issue. You'll need to find a way to keep it charging (using a hub generator as seen here) or have battery extenders (as seen in the millions on ebay).
Maps are downloaded from google maps so you'll need to have a data plan.