Filling cracks in a gravel/tar driveway with polymeric sand is a good approach, as it can help stabilize the surface and prevent further damage. The cost for polymeric sand typically ranges from $15 to $30 per bag, and you may need several bags depending on the extent of the cracks. It's important to clean out the cracks thoroughly before applying the sand to ensure proper adhesion.
For sealing the driveway, look for a sealant that is specifically designed for both asphalt and gravel surfaces. You can find products in the $20 to $50 range, but prices may vary based on your local market. Make sure to follow the manufacturer's instructions for application, especially regarding temperature and drying times.
Given that this is a community space, consider reaching out to local hardware stores or home improvement centers for advice on the best products for your specific situation. Additionally, if you're unsure about the application process, hiring a local handyman or contractor experienced with driveways can be beneficial.
As a next step, I recommend getting 2-3 local quotes on Handyman.com to find the best option for your budget.
— Assisted answer