I guess over time, all electronic items get cheaper. When recordable DVD machines first came out, they were circa £1200 but I've now seen them for under £500.
Working in the electronics retail industry, I see the prices plummeting on all such gadgets all the time. DVD players can now be picked up for less than seventy quid.
As for GPS, as new models become available, older ones will probably become cheaper before being phased out. I don't profess to being an expert in GPS, as I've only used mine twice. I think there's already a GPSV but I haven't seen a GPSIV.
I recently picked up a Garmin GPSIII (not the GPSIII Pilot) from an internet auction site (ebay.co.uk) for £204 including postage. Excellent little gadget, although I can see why some people could become overdependent on them if they don't practice basic nav skills too.
I tend to find out the co-ordinates of the places I want to use as waypoints (airfield from a VFR flight guide, and other places from streetmap.co.uk, which is great for precise co-ords). Plug these into the GPS and hey presto! - an easy way to plot a route, keep an eye on ETAs, off-track distances, bearing to waypoint vs current track, altitude and so on.