Despite what the web site says, I'd recommend Robertson's Dictionary, as the transliteration system is the easiest to understand. I haven't tried very many of the others, though including the one the web site author recommends, so he could be right.  Robertson's worked fine for me whehn I bought it back in the early 70s.

Can I get a copy in Asia Books?

Yes  you can www.asiabooks.com

And the price is only $5.44 versus the Amazon price of $25 new, but Amazon has used ones for about $3.60

look at learningthai.com

ORIGINAL TOPIC QUESTION: Are there schools in the Silom area?

I visited Berlitz Silom Language Center - first floor Union Tower - and picked up their fee schedule.

I will attend a Thai Language demo class on Friday next.

Many Thanks for all your replies.

I now have an idea of how much I don't know.

An interesting aside, however. Do you know that you get 150% corperate tax discount on training? Worthwile doing as many courses as you can!