You would need a custom tour/private tour in order to hike, and the prices for those smaller tours seem to start at about $170 per person. Would $100 be the total for both of you?
This is one custom tour company with lower pricing that has received positive comments, Mary Lou's Big Island Guided Tours. You have to contact them for pricing.
marylousbigislandguidedtours.com/About-Us.ht…
You really should rent a car.
I don't follow all the tours, but the excursions out of Hilo that cater to cruise ship patrons tend to either go north and do waterfalls and gardens, or they do VNP. Some go to lower Puna and Kalapana.
By the way, it is illegal for tours to take people to the Kaimu Black Sand beach at Kalapana, but some do it anyway.
Info on issue:
westhawaiitoday.com/sections/news/local-news…
You can drive there easily. It's a beach more for looking down on. Punalu'u is the best known and most beautiful black sand beach still existing, 40 minutes or so onward from VNP.
If you cannot drive, then you have to do what you can, but it will be a hardship not having a car, expensive, and you will not be able to see as much unless you plan on spending a LOT of money.