Airport parking is in a death spiral. Losing money because more and more people arrive via shared ride, e.g. Uber & Lyft because it's cheap if you live close enough. The initial reaction to revenue loss is to increase prices rather than cut capacity due to long-term leases.
Prices at places such as BOS are going to keep on rising until the private lots put their space to other uses and the market evens out.
People who drive a long distance to airports and can't really benefit from shared ride are going to bear the brunt of this.