I replace when technology changes or a meter goes crazy - bad values.
Time limit?? Batteries need to be changed every so often.
Cost - Most of the endos and a large number of family practice doctors have freebies to give out in their sample closets. ASK. I do not believe I have purchased a meter except for my copay on my Ping pump/meter/remote since about 1990. I also ask for calibration solution once a year and test my Ping meter and my backup meters (3 of them).
Learn who the local meter representatives are. Ask for comps. Every penny counts.