Just a few ideas to maximize your houseplant enjoyment, totally free.
1) Calibrate a hygrometer. Based on this excellent how-to article for cigar humidors, you too can turn your crappy analog hygrometer into a tool of fastidious precision! If you don't have a hygrometer, this is still a "cheap idea," because they are inexpensive and available at most hardware stores.
2) Save your favorite glass bottles and start propagating! It is definitely auspicious to have some tribute to PeeWee, the patron saint of vibrant homes.
3) Clean some humidifiers in preparation for the coming onslaught. If you plan to have one or several humidifiers running this winter for the benefit of your houseplants, it's wise to get familiar with the humidifier-disinfecting process. Otherwise your home will rapidly become redolent of Mrs. Whoever's third grade class fish tank. You know what I mean. If you are using a warm-mist humidifier (tut tut) don't forget to finish with a bleach dilution.
4) Pick up an interesting plant book from your local library.
5) Get creative with plants you already have. Try making a bonsai or topiary out of something unusual. I'm currently attempting to train a sansevieria to have curly tips. Think it'll work?