I'm really not sure what visa or extension you asked about and looks like you didn't talk to these 3 or indeed when you talked to them. Sure other cases like DTV costs more as does non b and others. I answered the OP question but friends in the past used thai visa service and Mots but not Tik tokwho are highly rated. The price is what it is on the day according to your individual circumstances why not call them and find out? Doing it yourself is way cheaper.
non O visa has many many reasons. Retirement and marriage are just 2. I suggest you read the Thai eVisa website as visas are always changing. Here's the link.