I place the pots on an old cookie sheet to catch any water spills. Therefore, I plant more vegetables than flowers. It helps cut back on my grocery expenses. Some plants are more costly to maintain than others. Many require lots of water, special fertilizer and costly pesticides.
Roses are a good example of a high maintenance plant.
Make sure that you know what your plants will require before deciding what to plant. Often manure comes with weeds or seed, but composting it before use will heat up the seeds and kill them. Mulch is free in some cities if they have a recycling program or a local public farm. Making your own compost pile will save you from buying expensive soil for your garden. There are books at the library that tell you how to start one cheaply and easily.