well technically i've done lots of visits to TH by air back to back with a week or two in between, and got told I should get a tourist visa "next time". So I wouldn't say its guaranteed to be 'no limit' for entries by air. I suppose you can do it until told otherwise.
Consider a tourist visa can be done online for $65, and you can then fly to KL and come back the same day, for less than $100 usd for 60 day + extension for another $60 usd, so let's say $250 usd every 90 days, or $1000 usd/year. Assuming you won't use one of these trips to go out and explore SEA.
Counterpoint to doing some edu/thai visa requiring you to spend time in lessons and the cost of the lessons themselves.
that's interesting because I've done bookings last minute, literally at the hotel counter, and Agoda was cheaper and thus we had to book 'online' first even though we were right there at the hotel.