Walking in France is a nice option, and any of the 4 main Caminos (Le Puy, Paris-Tours, Vézeay, Arles) would be a nice experience. They are all mostly hiking trails, that is to say mostly paths through nature, opposed to the Spanish Caminos that are most of the time along roads or looking like roads. There are also other paths you may find interesting, like the Camino of the Piémonts or the GR10 (the Pyrenee's crest trail,
not a
Camino de Santiago)
I've done Le Puy with 10€/day and Arles with 5€/day. Accommodations are more expensive in France than in Spain, but there are some affordable ones and (still) some donativos. It very possible to do it "budget-style" if you agree to camp. There are some camping grounds along the Caminos; a lot of accommodation owners agree to let people camp in their gardens for a lower fee; and it's easy (and totally legal) to do wild camping.
If you'd rather stay in Spain, you can start in Saint Jean Pied de Port then walk back and forth from the Frances to the Norte and end in Santiago. If you want to end in Santiago for the Compostela and not because of a plane you'll have to catch, why not walk one Camino to Santiago, then continue on another in reverse?
Accommodations are very affordable. In case you want to camp in Spain, know that camping ground are scarce along the Caminos and that wild camping is not always legal. Depending of the route you'll chose and the Autonomous Community you'll go through, it can be ok, not clear or simply forbidden.
I don't know what you think of by "scenic", but im-very personal-opinion, it makes me think of the Arles route, the Camino del Norte and Primitivo.
Buen preps