Not so weird; the demand fell away and so they're becoming scarce. They're growing to be priced similarly to sdcard carts for other old and far out of date systems.
Just have a look at what a decent cart for a Genesis, SNES or NeoGeo will cost.
Yeah, from my research the EZ Flash IV has some limitations(like max 2GB card support and miniSD only??), so the EverDrive X5 is recommended.....but that's £130 apparently??
It's expensive because of economy of scale. EZ Flash sells way more devices. However, it's more power efficient than the EZ Flash I believe due to better use of the FPGA. The Omega looks good though, and it also supports save states (nice for games like Harvest Moon FOMT where it's basically impossible to get all the best items without save scumming).
Just have a look at what a decent cart for a Genesis, SNES or NeoGeo will cost.