The Vista HCx is a good choice.
As has been said, the base maps are efectively useless for caching (and most other purposes). But while good maps on the GPSr are very nice to have, and I wouldn't be without them, you don't HAVE to have them. And whether you have them or not, the last 30 yards you just use the pointer, not the map anyway.
The Garmin Topo maps are medium price. The coverage is fairly consistent, but the detail is poor. You get contours, most roads and many paths, but no indication whatsoever about rights of way.
The openstreetmap maps are good value (i.e. free). They are inconsistent, but getting better all the time. Where they are good they have MUCH more detail than the Topo maps, but there are also large areas with virtually nothing at all.
Neither are as good as even a 50,000 OS map, yet alone 25,000.
If you want OS maps then you need an Oregon, or a PDA or phone that can run MemoryMap or similar. Price is high but results are good. Other advantages over the HCx are that you can run a more comprehensive cache database, and the displays are usually much better except in very bright sunlight. Disadvantages are that PDA/phones are less robust and water resistant than an HCx. The batteries don't last as long but are usually rechargeable.
I can go into lots more detail, but will only do so on request so as to avoid boring you if it is more than you want to know .
Rgds, Andy
Of course, if you find that the openstreetmaps are inconsistent or areas with no detail, go to the openstreetmap site and update the maps. That's the idea of a community. I't's really easy and you can even upload your GSPr tracks and trace those.
Many thanks to Talkytoaster for your efforts, they work great on my Legend HCx.
Andy K.