From a market perspective, SEO will not lower PPC bids - as more and more people enter the online market, they will only become more competitive and more expensive.
From your own personal perspective, then yes, having a strong SEO campaign can give you the ability to lighten your PPC budget (if we're talking just search engine PPC here). For example, if your keyphrase is "Blue Widget" and you're currently paying $1.00 PC in Adwords to be the #3 spot. Well, with a strong SEO presence you can get yourself to rank naturally for #1 for the search "Blue Widget". With that being the case, you may not need to be #3 in Adwords anymore, as most people have a tendency to click on natural listings before paid anyways. So, from that perspective, you could lower, or even eliminate much of your search engine PPC costs for the phrases you naturally rank well for.