I was under the impression that loans for foreigners are only through approved finance-linked new build moo-baan or condo developments. As the loan is through the property company and not the bank, they charge whatever they like.
Unlike many countries, Thai banks will usually not offer loans against land for property development. I approached a bank for a 1 million baht loan and they said that they would do this, but only if I deposited 1 million and they would then pay in instalments!
If your partner is Thai however, and they have land in their name, they can get a loan against the land through a government farming bank, the interest is low, but so is the total amount they will allow as a loan. 10 Rai of arable land might get you 500K, and the repayments should be around 8K a month, but payable at the end of every year.