If the "free" options don't meet your needs, here is how to get the most bang for your buck:

Navionics is the gold standard for marine navigation, but the question of whether you can get their premium marine maps for free is a common one among boaters and anglers. While the company operates on a subscription model, there are several ways to access their data without an upfront cost. How Navionics Map Downloads Work

It requires an internet connection; you cannot download maps for offline use. The Boating App Trial