I know that I can use arcGIS to display the USGS national map viewer (aerial, raster, topographical, etc), but I will be using API for commercial use and it would cost $4,000.
1) Can I use openlayers to display the USGS national map? If so, please provide a link.
2) Does USGS have an API? If so, please provide a link.
3) If there are no free methods of displaying the USGS national map, what is the cheapest method to accomplish this?