Just an update: got my Thai will written, translated to English and signed at a local law office for 6500 thb, gotta deposit it to amphur and have piece of mind on this matter. Whoever quotes 10k+ is simply trying to bank from your unawareness, just open google maps and call around for better quotes, took my wife whole 10 minutes to fine a good deal.
First overpriced lawyer was recommended by my wife's freind, but the friend's family is top 0.0001% richest family in Thailand, and I guess her lawyer is very well aware of that. Or maybe she expected a laundry list of assets to enumerate with all the labour involved, not sure.