As other PP's have mentioned, it's all about the discounts! And you have to keep watching for them. Here's my Dolphin discount story:
I decided to book a last-minute trip to WDW last December and I had missed the deadline on all of Disney's discounts for our travel period. I was traveling alone with DS5, so I still wanted something convenient, but not extravagantly expensive. I decided to give Swan or Dolphin a try, so I investigated a AAA discount at both resorts and saw I could get the best price at Swan, so I booked it - at that point, it was about $179 per night (rack rate at BWI was $375 per night for comparison). Pretty good savings! A few days later, the prices changed and Dolphin was offering a better discount, so I switched. In the meantime, I subscribed to the Swan/Dolphin thread here on the DIS, joined the Starwood Preferred Guest program (SPG) and kept checking the Swan/Dolphin website and Starwood site for more discounts. A few days later, I learned the Dolphin was offering a discount to celebrate the date 12/12/12 - rooms for $121!. One of my nights fell within the discount, so my price dropped again. THEN, the Tuesday before we left, I checked and Starwood had included the Dolphin in that week's "Starpicks" and was offering rooms at $132 per night. I called and got my other two nights dropped to that rate. By the time I checked in, I had found enough discounts to get 3 nights at the Dolphin for the cost of one night at BWI. I was ECSTATIC!
So, really long story short - just keep looking for those discounts, subscribe to the Swan/Dolphin thread and join SPG (oh yeah, because I was an SPG member, I also got a free room category upgrade and ended up with a view of the EP fireworks!)
LOVE the Swan and Dolphin!!