So I did some parts browsing and try to estimate the damage, but it seems the CX-70 FD would be the hardest part to find.

That being said, I was wondering if we can fit a 1x system in Dahon Espresso (say, a Shimano GRX 1x11 groupset)? If I got it right, we can use road bike brifters to pair with the GRX (as the GRX brifters are designed for disc brakes) and also need to find a wheelset that is compatible with 11-speed cassettes (Shimano RS010 maybe?). The downside to this path is that I have to sacrifice gear range as opposed to using 2x systems, but I think it would do for commuting and some planned light touring. Shimano GRX system are also newer so it would be much easier to find.