SatNav & PDA Advice wanted

I will keep this short and sweet for now. I am considering buying a satnav GPS device and, from initial research I think I would like a PDA version, rather than the more “normal” car mounted satnav system.

Obviously, as a poor blogger (feel free to donate 🙂 ) I am aiming for the cheapest one possible, but I still want to avoid a total lemon. Does anyone have any suggestions / comments on the topic? Ideally, I want one which is relatively easy to add new maps to (North America would be useful but not straight away).

Would a SatNav be better (more cost effective) than a PDA? While I feel I would like a PDA, I will admit I am not sure the extra functions will get used. The main reason for the purchase is to be able to navigate to remote places, I am not sure that being able to write a spreadsheet when I am there will be that valuable. Also, if I go for a PDA, would getting one with WiFi be worth it? It strikes me that a PDA without WiFi would be pretty pointless, the trivial task of bluetoothing data from my phone to PC is annoying, so I can only assume it would be worse with a PDA.

In a perfect world, I would be able to get the system for under £150, but I suspect that is massively over-optimistic, especially if I want a WiFi PDA. I have seen the MIO P550 PDA, which seems to have everything I want, for around £220 — does anyone know if it is worthwhile? Is there a Linux GPS PDA with WiFI? That would probably tick every one of the boxes as far as my buying wishes went 🙂