In general terms, is a Constant Speed Propellor equiped aircraft more expensive to maintain?
Yes, they are more expensive because they are more complex.  I would not avoid buying a plane simply because it has a CS prop because, in the grand scheme of airplane ownership, CS prop maintenance has a small impact on your hourly cost.  Maybe ~$1/hr for a piston single with repetitive ADs.

Now, the maintenance of a CS prop can range from a simple visual inspection of about \$100 USD to a complete replacement of the prop (up to \$15,000 USD, maybe more for large props).  An owner will likely not do an "overhaul" when the prop reaches TBO but will instead opt for an IRAN (Inspect, Repair As Necessary).  This is typically a little cheaper than a full blown overhaul and, from a practical perspective, extends the life of the propeller as an overhaul would.  At some point you'll end up grinding blades and balancing the prop but that's not annual maintenance.  I've seen the cost quoted at around \$1,500 USD for a high performance piston single IRAN which comes to less than $1/hr for a private owner.

All in, a CS prop only adds a small amount to the hourly operating cost.  In my opinion, the performance gains are worth the cost in most cases.