just to put a bow on this
bought a KuWifi bridge on amazon for $50. it took a little doing, but now have ~25 Mbps in the barn. Easily enough for the tv and podcasting I was wanting it for. Watched the 49er/Jets game outside the barn by the firepit, which was pretty sweet. And that's with both antennas mounted indoors - I have plans to move the barn one outside the wall to improve it.
it was a little frustrating setting it up, after a LOT of swearing and banging by head against the wall and many trips between antennas, finally noticed I'd plugged the host end into the back of my modem and decided to switch it to the back of the wifi router. instantly everything started working perfectly.
not sure why that fixed it, I assumed the "out" ports on the modem and router would be similar, but I'm not an IT guru at all
anyway, thanks for all the help!