Yes i did research all this before coming to this point. I also have Mega8 in the plans as it will just Cost about 20 cents more vs Tiny2313.I also have a Mega8 HID implementation with me. USB->Serial . The Serial > USB cables cost a little more than FT232L even when bought in quantities of 100's.
Also the thing is SMD increases PCB costs and The FT233L is itself expensive. Other wise its a very good solution. Also im planning to buy some Dip soldering machine to further lower costs , DIP soldering does not support SMD.
Our target is to Build a Affordable Robotics Platform for under USD 20 which would include everything. And the Serial Boards are to be made in around USD 4 - 6 and USB ones around USD 7 - 9. These costs include minimal profit.
We are trying to keep costs minimal, As in India for my target audience USD 20 is a big amount.
So for the USB board im searching for decent yet cheap alternatives for USB->Serial.