Ekso,
Do not concern yourself overly with the base map - it's pish! ...and that goes for whatever unit you settle for.
Assuming you are looking for a unit that will store hi-rez maps, when you install them, as you will eventually want to, the hi-rez maps are displayed instead of the basemap.
Shop through eBay for a good deal but do your research first - new units can be bought at reasonable prices from European sources. I got my Vista C from:
Aspidshop...
...based in Portugal I believe. The unit arrived at crack-of-sparrows the very next day. Cheaper, faster - and a European unit too.
Just had a look as site myself. It's fantastics. Alrady on my favourites.
So, whwt you're saying is that if the basemap does not matter, should I get one from the US. I have friends that come to the UK regulary.
Lastly, which one !! Garmin Vista ?