How do you get there? If you want "well-below-market money," you have to decline the club options and pay the buyouts.
When you do that, McCutchen is a free agent. If he's limited to "well-below-market money," what makes you think he would choose to sign with the Phillies? He can probably get a short-term, below-market offer to play LF part time and DH from... the Pirates - which he would take in a Pittsburgh minute! If he's all about the money (which McCutchen is not, fairly obviously), do you think the Phils would be the highest "below market" bidder?
If you buy out Herrera, he's eligible for arbitration. He was paid $10 million this year, and he has 5+ years of service time. His arbitration award would exceed $10 million, on top of the $2.5 million buyout. The only way you get to a "below market" deal with him is to buy out the option, non-tender him, and somehow outbid everybody else "below market" for his services.
These aren't realistic expectations. IMHO, the Phils' real choices here are binary - either exercise the options, and pay eight-figure salaries to these two, or say goodbye to them.
I agree about Didi - to get rid of his contract, we'd have to pay somebody to take him - payment likely not just in cash, but in some prospect we really can't afford to lose. As annoying as it may be, I think it makes more sense to just pay him what he's owed (whether on, or off the roster may be almost immaterial) and be done with it.