You can always start with tiles from https://openstreetmap.org Or use one of the commercial providers which offers free tiers. There are quite a few smaller providers that are not super expensive.

You can always setup your own tile server. It's not that hard and can be cheap (if you don't count your time). I recommend, checking https://github.com/onthegomap/planetiler

I used Deck.gl and CARTO basemaps. https://deck.gl/docs/api-reference/carto/basemap

You don't need a token to use this map, as long as you keep the usage to a reasonable limit (I think it says 1,000,000 tiles per month)

Mapbox GL is pretty reasonable, or even free under 50K loads.