Many come to Thailand and enter as Visa Exempt or using a Tourist Visa. If you qualify for an extension of stay based on retirement, you can "apply" for Non-Immigrant O Visa if you entered Visa Exempt OR you can apply to convert your Tourist Visa to a Non-Immigrant O Visa. If in Pattaya, Immigration on Jomtien Soi 5 takes the application and required documents (passport, meeting financial requirements, residence, photo) plus fee of 2,000 baht - documents are sent to Bangkok for approval and a minimum of 15 days on your permission to stay needs be available - otherwise, you can extend the Visa Exempt 30 day initial stay or Tourist Visa 60 day initial stay for another 30 days. Thai Immigration does not require a police report or medical certificate as part of the documentation.
When approval is received, Pattaya Immigration places the Non-Immigrant O Visa in your passport and gives you a 90 day permission to stay from date the Non-O is issued. After 60 days have elapsed, you return to Immigration and apply for a one year extension based on retirement -- same documents required, application for extension fee is 1,900 baht. The extension is issued by Pattaya Immigration, they usually ask you return the next day to pick up the passport.
As to "buying" a Visa - hmmmmm! The form says Application and as I recall, most Embassy/Consulate websites, dealing with Visa applications note that fees are not refundable in if the application is denied.