Yep. Cogs are generally less expensive than chainwheels. For up gearing, I'd usually recommend going to a smaller cog if possible and removing a link(s) of chain rather than spending more for a larger chainwheel and buying a new, longer chain.

In an almost unbelievable convergence in the industry, Shimano 3-, 4-, 5-, 7-, 8- and 11-speed, SRAM 2-, 3-, 5- and 7-speed and Sturmey-Archer 2-, 3-, 4-, 5- and 7-speed IGH cogs are pretty much all interchangeable (there are a few exceptions and limitations) and interchangeable with the cogs on many single-speed coaster brake hubs. These three-tab standard cogs are available from 13T to 24T for 1/8 and 3/32 chain in flat, dished and deep dished patterns.