I don't think fiber cables are expensive. I ran CAT6 in my house and at the same time pulled an OS2 single-mode 30m fiber cable to my office for core switching. The 30m fiber cable was $17 on Amazon, plus two 10G-LR modules at $18 each. The equivalent CAT6 is more power hungry, has less range, the cable is the same damn price, and the 10GBase-T SFP->RJ45 transceivers are twice the price of the LR transceivers at $50 each.
Infiniband uses its own cables with dedicated/integrated transceivers. It's not compatible with Ethernet and can't be swapped (unless you plan to talk plain Ethernet with your IB card, which is possible).
A 5m, 200gbps cable is $1,149.00 a pop [0].
Mind you, this is neither the longest, nor the fastest cable.
