Even on a one day tour, why do you need a tour guide? Get a TCI map of Tuscany, rent a bike in Lucca, and go for a day trip north of Lucca. Use a train to get yourself and your bike to the starting point, then ride back, or ride to a town with a railway station and take the train back. TCI (Touring Club Italiano) regional maps are great for planning cycle tours, get them here:
www.trektools.com
Lonely Planet has an updated version of their cycling guide to Italy, here:
http://www.amazon.com/Cycling-Italy-...7060834&sr=1-1
Rough Guide does excellent travel guides, they're not cycling specific but the authors understand about low-budget, active travelers. The current Rough Guide to Tuscany would be a good source for ideas of where to go.
Seriously, forget the tour guide, get a phrase book and some maps and strike out on your own. Once you get away from the standard tourist areas, Italians are very gracious about helping lost foreigners, especially if you make a minimal effort to speak Italian (even if it's just "parla Inglese, per favore?").