The Small Business designation is for those just starting out or for those who have "fulltime day job" positions and are making parts on the side/evenings. This provides added opportunity to promote your products with some Vendor benefits without the added monthly/yearly costs.
Simply, the Small Business upgrade includes:
Monthly subscription cost: $10
This is NOT designed for full time businesses, but rather for the weekend/evening fabricator who is offering their skills and products to other forum members, or for those just starting out with a new venture who are unsure of their business future. Hopefully, business grows exponentially :-)