I took roughly 15,000 Baht for training and accommodation, including pickup to-from Phuket Airport. There's a cafe and convenience store right next to (and owned by) the gym where I ate everything before and after training. A decent meal was 50-70 Baht. Getting an electrolyte drink and energy drink added a few extra costs as well, but unless you're going out to Patong and parting all the time then your stay will be ridiculously cheap.
My total budget for non-training and non-flights for the month was 10,000-20,000. I didn't do much partying, and ended up just buying two sets of gloves, shinguards, couple of shorts, t-shirts, etc with my excess money.
You can negotiate with the guy who administrates SuWit to get your meals included in your fee. It's good food, but eating it constantly will be grating. But like I said, around the corner is the Tiger Muay Thai / Phuket Top Team "infrastructure" that hosts a lot of restaurants and bars. Including a pretty good barbecue place.
And I'm not sure about 1 on 1, seeing as how I noticed pretty much everyone there including myself was getting 1-on-1 training. My instructor was taking care of me and another guy. When he held pads for me, the other guy would just do bag work, and vice-versa.
I was flying from Taipei, but even still my flights were the biggest expense.