What's is the right place to get some t-shirts printed?

Is it MBK?

And do you think I can buy the shirts at the print shop? (Don't want to spend a lot of time with shopping, it is for a birthday joke)

Thanks!

you got it, mbk is the place.

MBK 4th floor Namfon interprint.

1 t-shirt + with 1 colour print (letters) 500 baht

40 t-shirts 250 baht per piece.

I still keep my eyes open for a better shot.

There's a shop/stall at Union Mall in Lad Phrao that does all sorts of lettering and anything from the simplest of designs to detailed caricatures, all printed onto T shirts. It's easy to find. Take the MRT to Phahon Yothin. Leave the MRT station at exit 5. As you come up to ground level from the MRT you'll see a (small) set of escalators/stairs in front of you leading up to the first floor of Union Mail. Once you get to the top of the escalators follow the walk way into the mall. The place you want is not far in, on the right. Just before the 'Mr Bun' cake stall.