Their value is based on their condition and what someone is willing to pay. You should be able to get in excess of $50 per mag, but how much more depends on too many factors to give you a good idea. I would definitely sell them on an AUCTION board, though.
These were the 2nd earliest commercial mags for the AR15, before it even became the M16. The very first mags were 25-round mags, but only a tiny number were made. The 20-round waffle mags were used by the SEALs and the Vietnam "advisors", until they were replaced by the more conventional 20s you're used to seeing. The waffle mags were not very reliable, which is why the design was changed and the extra ribs removed. Because most were destroyed (due to being unreliable), the remaining mags are rare today and are highly desired by collectors.