If you can find a K20z3 (stock TB) for cheap you can have it bored out via Maxbore for $100. You have to pay to ship there but return shipping is covered in the cost.
I picked up a used z3 TB for $60 and shipped it to Maxbore for about $14 and paid $100 for the service. So about $175 for a 64mm throttle body. I've seen the stock TSX TB go for $200+ usually so this may be a cheaper alternative for you.