Hello
@Leemac40
Welcome.
It is a good many years since I did the Baztan route, but I didn't find expense then to be the problem, except for the first night in Espelette, where the municipal hostel seems to have been closed for a long time, not always for the same reason. There is a tourist office in Espelette (it is quite the tourist town) and you could check with them for other options.
Have you checked
Gronze here? Having a quick look, there seems to be a reasonable amount of accommodation, including albergues, although again Espelette is limited. It is a more useful option for information than the online booking sites.
There seems to be a steady trickle of people doing the route at the moment, so you may get some specific up to date recommendations. But it is a trickle!
I have never used a tent, so cannot really help you there. But the Baztan route can be very wet.....!
Tim