What are the costs and requirements for renewing a DTV Visa in Thailand after 180 days, and do I need to submit my 90-day report at the same time?

You shouldn’t have a DtV if you dont know how it works. You have to leave the country get stamped out and then return there is no fee for this. No renewal. Just every 180 days you have to leave. Yes you can do this at immagration also but it is a royal pain in the butt and some immagration offices will not do it because it a pain. Just leave and come back. And no in therory you dont have to do your second 90 days report because you have a grace period.

You're better off leaving and re-entering rather than applying for an extension. You will need to essentially re-qualify for the DTV and show new current proof again.

You do not renew a DTV, but you can apply for a 180-day extension for 1900 baht at immigration with largely the same documentation requirements as for the original visa application, including proving 500 000 baht in your account. In practice, very few people choose to do this, and most simply leave Thailand briefly or do a border bounce to obtain a new 180-day stay. This can be done as many times as you wish within the five-year validity period of the multiple-entry visa. You must file a 90-day report each time you have stayed in Thailand for 90 consecutive days.

You don’t renew a visa.