I saw this one the other day but I have no idea how reputable they are. That said, I hear people on here rave about how good TikTok Services is but I've never used them & I don't know their prices.
I didn't read all the comments so maybe this has already been addressed but technically you need to have the equivalent of 20,000 Thai Baht in cash & proof of where you'll be staying (e.g. Proof of hotel booking.) BTW,the 20K THB can be in ANY currency (e.g. GBP, USD, EURO, etc.)
exactly what Nigel said, cash only. When I land here I always arrive with extra cash (it never hurts to have extra cash.) Looks like you're in the US. That said 20K THB = nearly $550 USD right now so I'd bring maybe $750 USD to allow for any exchange fluctuations.