You should be able to get a brand new HP-505 for the same price. I would prefer the newer HP-505 then. While sound and keyboard are the same, it has technical advantages, besides the better pedal electronics it is better prepared for the future, in my opinion. The disadvantages of the 505 in comparison to the 307 is the not as bombastic loud speaker system, but I would say that this is not such strong argument as the electronic advantages of the 505.
Decide if you need to be prepared for the future and for that case go for a 505. If you don´t need to think about the future, but just want that perfect keyboard action for a good price, then check what your dealer wants for a 503, and take this as the todays value of a new 307. You should not go for the 503, though, just use it for calculating the 307 price in order to get it clearly cheaper than a 505.