hi - there’s no fast way overland, and SJPP is a small town isolated in the mountains, so overland trip will likely be 24 hours of slow train/multiple bus connections. Couple of suggestions though -
1) try ending your flight in Lisbon or Porto. You can walk from either city to Santiago (both great caminos) or connect to Biarritz (BIQ airport code) which is closest to SJPP
2) do an open-jaw flight into Madrid and out of Porto on TAP - you can take bus from Santiago right to Porto airport
2) try extending your TAP flight to Madrid, and take excellent buses right from the airport - or if you overnight in Madrid, compare trains and buses to Pamplona, and then take 90 minute bus to SJPP
3) connect from Santiago to Biarritz airport, then 90 minute train to SJPP
4) connect from Santiago to Bilbao (airport code BIO), and start either at Logrono (60 min bus), Pamplona (2 hour bus) or go to Pamplona and then 90 minute bus to SJPP
5) consider starting in Pamplona instead of SJPP. It’s a very popular starting point for Spanish peregrinos and it’s only 5 hours by bus or train from Madrid
i highly recommend the Spanish bus system ALSA, they are fast, inexpensive and buses are very nice. You can prebook bus on ALSA app - set up a BusPlus account and input your info to book right from the app (available 60-90 days before departure) - non-Spanish credit cards may not work, but link BusPlus to your PayPal and it will work
Hope this helps and good luck