A quick Kayak search tells me that a one-way ticket from DEN-BOS would be over twice as expensive as a coach fare ($421 vs $196 on AA) if you wanted to leave on Saturday.

OP, you should be aware that domestic first is nothing special these days, with the only real advantages being a slightly larger seat, free alcohol on board, and possibly a meal depending on trip length. Personally, I'll take the upgrade when offered to me (via FF status), but I wouldn't pay the premium to buy F outright. Maybe it's worth it to you, but you should be informed and set your expectations accordingly before purchasing.