The lawyer was very vague about costs.
I did it a decade or so ago and as far as I know the prices to the Thai government haven't changed since then.
When you initially apply, the non-returnable fee was about 8,000 Baht.

Many months later, maybe a couple of years, when you are accepted, the government fee was something like 181,000 Baht (half if you are married to a Thai) and, I think, not chargeable if rejected.

The amount of documents they need are enormous and I think someone to guide you through all this would be invaluable.

I looked, on the year that I was accepted, at the list of successful applicants, and in the countries that I looked at --- nowhere near 100 applicants from each.

The P.R. HAS TO get a re-entry permit if going abroad on holiday etc. so not all visits to Chaeng Wattana are avoided.