2 thermostats week on week off
A thermostat is basically a few contact closures that are controlled by a temperature switch and a schedule (on programmable models).  You can split the wires going to your single thermostat and run them in parallel to more than one thermostat.  Your plan will work and with the cost of 7-day programmable thermostats, it's probably the cheapest option.

However, as others have noted, WiFi thermostats are the future, and if you have a C-wire available (search this site for tons of info on C-wires), they can be great.  Nest is not the only "smart" thermostat available, and I for one do not like the way it claims to "learn" my schedule.  I use a cheaper WiFi thermostat that can be programmed just like traditional models to very specific times and temperatures without any guesswork.