Theme pricing is up to the developers of said theme. There are many nice free ones you can try. So, four options here...1) reuse themes you've already purchased, 2) search for and use free themes, 3) pay the higher prices but buy less themes, or 4) don't change your themes so often. $3 for a theme seems like a bargain considering the time spent designing and coding the theme.
People think everything related to software should be free, for some reason. Probably due to early computing, where there was a lot of shareware and freeware.
