Compared to other renewable energy sources, available bioenergy supplies are relatively constrained by the land resource needed for production. Bioenergy costs can also be expected to increase if less productive lands are put into use, since production costs are likely higher on such lands. This study develops a method to estimate biomass crop costs at different delivered quantities. A geographic information system model is coupled with a crop-growth simulation model (ALMANAC) to provide information for an economic supply function. The method provides a high degree of resolution, appropriate for regional biomass crop research. The approach is particularly useful where no biomass crop industry exists, and/or where land resources are heterogeneous. An example of switchgrass supply potential in western Massachusetts is presented.