Visa is £115 plus any associated costs such as biometrics , return of passport to Thai address , translation and copying. This is if you do it yourself. Agents want more but still can only submit the same paperwork
A lot easier if you had got married in Thailand. You would still need to get your marriage certified each year for visa extension purposes, making sure you are still legally married
Did you submit your own bank statements showing financial stability and liquidity, a hand written and signed letter stating you intend to fly both ways with her and pay for all her outgoings when in the UK, a copy of your own passport, names of her mother and father and any of her children in Thailand ( this part MUST be included in the application).All property deeds that she owns translated, including house book.