Look around at some of the "travel hacking" websites for ideas on how to bring the price down. You can probably afford to do both Italy AND Napa if you put some time/effort into it. Travelling in shoulder season instead of in summer is tip #1. Sign up for some credit cards with frequent flyer bonus miles to get at least one ticket for free (free seats are much easier to get outside peak season). Consider home exchanges (as someone else has mentioned) or air b&B, etc.
Happy travels!
Happy travels!