Most state societies no longer require a sponsor and they welcome new members. If you encounter a Society that requires a sponsor, ask the State Historian to sponsor you. Joining the Mayflower Society is relatively straight forward, as long as you have a well-documented line back to about 1900 — meaning you must acquire birth, marriage, and death certificates (hopefully ones that identify parents). These are sometimes expensive. If you or someone in your line had multiple marriages, you have to document those as well. Application fees vary from state to state, as do the annual dues.
The first five generations are well documented and Mayflower Silver Books now cover most families up to the line carrier in the 6th generation. For the most part, that covers the period through the American Revolution.
The major problem most applicants encounter is the sparseness of records for generations 6 through 10. Census records did not explicitly identify family relationships until 1880. Also, fires in court houses, churches, and Chicago destroyed many records.