Always cry poor mouth. Tell her about all your expenses that you have back in your home country and how you are looking after relatives etc. etc. etc..
Offer 12,000, that is a win-win for both. Twelve thousand for a month of fantastic sex is a bargain. If it doesn’t work out, no problem. If you advertise that you will support a Thai lady for 30,000 a month you will have a queue from the airport to your accommodation wanting to come on board