Rules question:
Your hand: Laboratory, Bazaar, Poor House, Copper, Copper.
Play Laboratory, draw two Coppers. Play Bazaar, draw another Copper. Your hand now looks like: Poor House, Copper, Copper, Copper, Copper, Copper, and you've already produced $1 to spend from the Bazaar.
Now play Poor House and all of the Coppers. How much do you have to spend now?
Option 1: $6. You got $1 from the Bazaar, $0 from the Poor House, and $5 from five Coppers.
Option 2: $5. You got $1 from the Bazaar, $-1 from the Poor House, and $5 from five Coppers.
What I'm getting at is that I'm not sure if Poor House's $0 minimum means that Poor House can't produce less than $0, or if your total coins to spend so far can't be less than $0.
Poor House can net you negative coins. Option 2 is correct. Donald has confirmed it at BGG.
On BGG, Jeff Wolfe (one of the Dominion playtesters) gave this example:
"(assume Council Room or something)
Play Market, you have 1 coin to spend
Play Market, you have 2 coins to spend
Play Poor House and reveal 5 Silver cards, you have 1 coin to spend
Play 5 Silvers, you have 11 coins to spend"
(End of Quote)
So it appears that Poor House only reduces the value of money you have gained from the previous action cards you played before Poor House. Once you start playing your treasures, it does not affect their value. And Donald X. gave a thumbs up to Jeff's example.