Does anybody know how much it would cost to hire a clothes designer? An estimate would be nice. And I'm talking about by project, like for example, to design a shirt it would cost so and so. Thank you.

I don't think there is a "union scale" for apparel designers n Thailand. I suppose you could get a design student from a reputable school to design a shirt for a couple of thousand Baht, or an acclaimed fashion prima donna for a few hundred thousand. As a general rule you're looking at a daily rate of around 1500 for a professional freelancer in the design field.