Originally Posted by Jipe

Their bike cost more than a Pacific Cycles Birdy R with also 20" wheels, disc brakes, internal cable routing...

The pictures are very small, its difficult to see how this bike is made.

But what I can suggest:
- First put the mounting point for the Birdy folding rear rack (they should be placed at the right place to allow the rack to fold when the rear frame is folded). The bike of the picture doesn't allow the mounting of this rack.
- Use an asymmetric main tube to minimize the folded size like Pacific Cycles did on the real gen 3 Titanium Birdy.
- Make a rear frame and fork that accept 50mm wide ETRTO406 tires ( it not possible with the real Birdy frame, the max tire width is 32 to 35mm depending of the tire type).

One more remark: building a titanium frame is very different from building an aluminum frame, soldering must be done in inert gas to avoid any oxygen contamination that would make the soldering corrode and break after some time.

I have no idea of the used price of the very limited series gen3 titanium Birdy. Its price was 6500USD without import taxes and without shipment (its the price I paid buying it directly from Pacific Cycles). There was one for sale on the forum (located in the US), as far as I know it wasn't sold.