Once your 90 days is up step out of Thailand for a few days. Fly down to KL for a couple of nights then return to Thailand. You will get another 60 days visa exempt entry and then extend that by another 30 days. 180 days all up.
I must be doing something right. As I said I have never been pulled aside..and I have routinely carried a lot of cash thru immigration. I will continue to do so. It is mine. Ive earned it and I paid tax on it.