As has been explained before this is a painless procedure as long as you have family/friends in the UK.
Firstly you have to book online, if you can print off the receipt with the FCO in Milton Keynes and pay their fees. 30 quid for the notarising and apostille then 5.50 for it to be couriered to the Thai Embassy. Send 2 A4 envelopes, one for courier to Embassy and second for Embassy to family/friends.
Secondly this is where family/ friends come into play. They will need to pay the Embassy by cash or postal order the sum of 10 pounds. Then the document will be sent to them when completed. Ideally you need to email the Embassy to inform them of the arrangement. Family/friend is paying by postal order to have this document of mine stamped.
They then use DHL or whatever to get the document back to you in Thailand safely. Cost is about 50 pounds.
Takes between 2 and 3 weeks to complete depending on the post to UK.
Then all you need to do is go to the MFA, get it translated and stamped there. Costs are around THB 2000 depending if you want to wait or use an agent to do everything for you and post it to you.
Easy to do yourself as long as you have computer, printer and good family/friends in UK. Lot less than 500 pounds.