Personal experience of touring in Portugal is not great from a bad traffic not-used-to-cylists point of view. It did get better the further I got from Lisbon however. I've done more touring in Spain which I have found a lot better (from this point of view, don't get me wrong, Portugal is a great country.)
You could consider doing the Camino de Santiago in Spain- if you do, and get a pilgrim passport, you can stay in refuges (like hostels but cheaper) which generally cost around €5. It is also a really great route indeed.
Campsites are very cheap in France if you stick to the municipal ones, cheaper than Spain. In Spain they tend to be more popular along the coast.
Other than that Spain and Portugal will be a lot cheaper than France and Italy. I would estimate cost descending in this order: Italy-France-Spain-Portugal (especially if you are touring in northern Italy.) Rural areas and small towns will be a lot cheaper than cities, while the north of all countries will be more expensive than the south, particularly in the case of Italy and France. Cost will drop over the Spanish border and further decrease as you head west to Galicia (recommended, especially in summer) or south to Andalucia (cycling in central Spain prob not a great idea in mid-summer.) Portugal will be cheaper still.
Generally pensions (guesthouses) will be cheaper than "backpacker hostels" in Spain and Portugal and you will get your own room (e.g. you can pay as low as 20-25 for a room sleeping two in a pension, but 20/person for a dorm bed.) Ask for one without a bathroom (or TV) if you are trying to negotiate the price down!
How long are you going for?