True, in terms of price, duplex is cheaper (though compared to overall router cost that is negligible). In my case, I wanted to be able to swap SFPs if input one dies (for any reason), and it doesn't make a lot of sense to buy different modules for different purposes, even if that would save a bit of money.
There is another difference - if I want to go for field connectors and cut it myself, the Simplex connector would cost about 4.15$, and the Duplex would be 6.16$, which would further increase the price difference.
But thanks for the advice, it is indeed a viable option.
The price of 25GbaseT (rj45) is still very high. 10GbaseT (rj45) is coming down very nicely though and some motherboards, routers and high end access points have 10g ports onboard. I think it's actually cheaper to go 40gbps QSFP and run MPO cables (4 pairs internally) than it is to go 25g fiber. This is pretty much the case in datacenter right now for anything that doesn't need to go over 300M.
I think it's actually cheaper to go 40gbps QSFP and run MPO cables (4 pairs internally) than it is to go 25g fiber.
It's not. 25G and 40G transceivers cost the same and MPO cables are more expensive.
If your concern is the physical size of the cable just make sure you're getting a non-splittable duplex cable. Some people prefer splittable because then if they need a simplex cable they can just pull it apart but that's what requires the cable to be larger as you get 2 individually shielded cables. The actual fiber core is measured in microns, you can pack 100s in roughly the same sized jacket.
Bonus note: If you're ever looking at doing a bunch of runs between two spots you can look into MTP/MPO trunk cables. These put 12 strands in the same protective sheath so it's still a really tiny cable and then you can break out via a pigtail cable at the other end.