I realise you can get one with a hire car while out there - but looking at the cost of doing so, it seems it might be better to get it all here, and then I'll have my own sat nav to show for it 
(I don't actually like sat navs and prefer to make my own way, HOWEVER I can't trust I will be able to do that in Cali, and using Google maps on my phone when I inevitably get lost will cost LOADS in roaming data charges).
So anyway, I hear the Navigo is a good bet, as it can load TomTom software? Does that sound like the best route to take (pardon the pun)?
Any recommendations? Trying to keep it as cheap as I can get without coming out with a hunk of useless plastic.

(I don't actually like sat navs and prefer to make my own way, HOWEVER I can't trust I will be able to do that in Cali, and using Google maps on my phone when I inevitably get lost will cost LOADS in roaming data charges).
So anyway, I hear the Navigo is a good bet, as it can load TomTom software? Does that sound like the best route to take (pardon the pun)?
Any recommendations? Trying to keep it as cheap as I can get without coming out with a hunk of useless plastic.