Thank you! I actually just migrated walking directions to self-hosted graphhopper instance which should cut about $25,000 from that estimate.

Now I’d just need to find a suitable replacement for map tiles, place search, elevation api, and rewrite the app.

Thunderforest is a great start for tiles. I'm not aware of a discrete elevation provider, though Graphhopper can be made elevation-aware, I believe. Place search is more difficult (if you're thinking POIs) and it might be worth investigating Foursquare etc.