Hi Marshall,
To start the process it is easy and doesn't require more than an hours time. You register and add your site. The cost is roughly $100 USD. (per site)
After you set up your account and add your site there will be an option to answer an SAQ (Supplier Assessment Questionnaire). This is what your customer wants to review.
The questionnaire is best answered by the Human Resources Manager and the facilities Operations Manager. The questionnaire can be saved in process and once the team members are done with their part at different times. For the company I work at it took the two team members an afternoon to complete. For the 20 US suppliers we work with that were tasked with the same request it took from one day to a week (they were working out the set up and who was responsible to answer questions).
Once completed and saved you will than accept a "relationship" request from your customer where they will have visibility to your questionnaire. Based on your answers the customer will perform a risk assessment and may or may not ask for an audit to be performed.
The audit is an onsite audit and typically takes about 3 months to secure a date in the US depending on the certifying body you use (we are limited to auditors due to the certifications required, most are coming from other countries). The audit itself would require again the Human Resources Manager and the Operations Manager. The audit is focused on the employees, labor, and the health and safety practices. The audit questions are available online for review. The average costs I've seen is about $3500 (that includes the auditors costs for travel and stay).
I've worked on the SEDEX platform for many years, and have completed a handful of SMETA audits. Personally I think the SMETA audit is a great addition company to have because it identifies areas in the operations just as important as food safety and quality that get overlooked. There is a US customer service contact at SEDEX if you have further questions.
Good luck!