Electronic tolls in Portugal

I am not sure why you think you can get a 'best deal'.
A google of 'electronic tolls on roads in Portugal' or similar should give you the accurate information you need.

Let me beg to differ that it's easy to work out the story on the electronic tolls. We recently rented a car in Spain, intending to drop it off in Portugal. The international rental agency told us to stop at any gas station just over the border to rent a transponder to register the tolls. That might work for a southerly route. But it didn't work at all for a border crossing mid-Portugal. None of the three gas stations had any such rental transponders.

Online, we also saw information that you can pay the tolls by showing up at any Portuguese post office, at least 48 hours after accruing the tolls and pay them there. Except that at the two post offices we went to, we were told that was impossible. We finally went to the post office at the Porto Airport--if they couldn't help us, no one could. And they shrugged and said nothing could be done with a Spanish license plate.

So, in the end, we wasted lots of time trying to figure things out online, got lots of incorrect, outdated, and confusing information. And still didn't get the tolls paid. Luckily, most toll roads still have toll cards and manned booths. But we did rack up some electronic tolls...So we'll see what turns up in the mail from the rental car company someday.

It's pretty simple and can certainly be done with a vehicle with non-Portugese plates. There's no 'good deals'. Two systems exist: Via Verde and Easy Toll.

Here's an explanation: http://www.thebarefootnomad.com/travel-tips/the-ultimate-guide-to-toll-roads-in-portugal/