Your costings are correct. Embassies do a mark up on the 10K THB so you need to check the actual cost on the embassy site you apply from. 1900 for extension but it is much easier to do a border hop. Can take around 10 business days.
It is fine to put you are unemployed. More embassies want to see how you can support yourself on SP hence employment info request. You can submit additional savings , investments etc to show your financial independence.