There are more campsites than it appears at first glance, all the ones I stayed at were lovely and very clean. There are quite a few campsites along the coastal route.
I stayed in Lisbon first couple of nights and took the train each day (I think you can camp but I enjoyed the hotel).
Tomar:
https://campingtomar.wordpress.com/ - you get free entry to the outdoor pool next door.
Santarem, I don't think you can camp here, I stayed at this lovely place:
http://santaremhostel.blogspot.co.uk/
Golegã
https://en.camping.info/portugal/lisbon/parque-municipal-de-campismo-da-golegã-16364 very friendly place
Coimbra -
http://www.coimbracamping.com/index-uk.html (I didn't camp here)
Viana do Castelo - I camped at the first campsite by the bridge. The chap who is runs it is really eccentric. The showers and toilets are in the stable block (some of the stables have horses in them) and there's no top to the stable door so you have a view when you shower
. Not everyone's cup of tea but the place is kind of fun. There are peacocks wandering around.
I didn't camp as much as I had expected to, in a couple of places the campsite was on the edge of town, you need to walk into town to get key , walk back and then do the trip again for an evening meal adding about 6 miles onto the day's walk. I snore so not really an albergue person but I found ensuite double rooms for £15 in a couple of places. Also, some places reduce their costs in the evening, I was walking quite long distances and found one place on booking.com that was £65 in the morning but by 6.30 pm it was down to £15 for a luxurious ensuite double with air con.