Since the new MBP price dropped it's hard to say. Before on the refurbs you would see between $100-300 less if the Refurbish is over two years old (from the build date). MBP Unibody 08 list for $1299 for 2.4GHz (Original priced $1999). Current MBP 2.53Ghz SD list $1699 new and $1499 refurb. So with that in account this model a year from release, which is after 2010 June, refurb would drop to $1299.
From memory, I saw this happen with the early MBP 08 models, however Mac was selling them for $1599 refurb. Then after MBP Unibody were released, the price dropped to $1399.
But honestly since the MBP are now cheaper, I can't see Apple dropping the price any lower than $1299 for entry level MBP, $1499 for highend MBP.