To extend on what fcolor said, PPC is a form of SEM (Search Engine Marketing) that is an off-site advertising element in marketing a website. SEO is an on-site element that is also required in marketing a website. In my opinion, SEO must be implemented in order to run a more effective PPC campaign. The better your SEO, the higher your conversions with PPC will be. SEO and PPC work together.
It can be argued that the only measurable advantages of PPC over SEO lies in the control of 3 areas: Relevance, ROI & Reach. I say this because the tools offered by e.g. Google Adwords for PPC offer controls that allow for precise targeting of a market as well as quick turnaround in making adjustments to a PPC campaign. This can result in high ROI when planned and managed properly. A good SEO will however be able to measure and manage the same factors and make adjustments to a website as well, but the results might take a bit longer to show in organic listings.
In terms of your comments, I briefly assess PPC v. SEO as follows:
- Setup time and costs are variables in both fields. Both need similar research and time and costs are too dependent on the specific campaign/budget to compare.
- Both fields can offer the same long term value, as long as the targeted keywords are still relevant. The PPC value ends when the ad campaign ends and a target has been met which is based on the PPC campaign. The SEO continues to work for the website organically, as long as the website is live.
- The risk is the same for both fields and is tied into the cost for each. If the initial research for both SEO and PPC is poor, then it will cost money. However, a poorly managed PPC campaign can bankrupt you overnight, yet poor SEO can not.
- PPC does offer quick measurability on performance monitoring and conversion tracking, but a good SEO will be able to report on the same with a little extra work. Understanding analytics is the key to both.
- PPC is flexible yes, but so is SEO in making on-site adjustmentments and adding/changing content to a site.
- Implementation in both fields varies but there are many similarities in e.g. the research and campaign planning beforehand. Once the groundwork for either field is done, it really depends on the size of a campaign.
The biggest difference between PPC and SEO lies in the impressions and clickthrough rates (CTR). With PPC you have a limited number of impressions that you can achieve within a set budget. Generally speaking, you have a higher CTR on PPC impressions, since you are targetting a very specific type of search query and you are almost guaranteed a certain position on the search results page for your targeted keyword(s). Organic listings achieved through SEO (and other SEM practises) have variable CTR, depending on the position of your listing within the first few results pages. However, with SEO, it is possible to achieve consistently high search engine results that could produce much more impressions without being limited to the budget constraints of a PPC campaign. So, in defence of good SEO, for the same amount of budget, you can potentially get much more impressions, for the same targeted keywords, which even at a lower CTR will translate into more qualified visitors to your website over a much longer period than PPC can do. In defence of good PPC, I will say that it can offer results in a short period of time with a limited budget, resources, experience etc. PPC is advertising and, after all, advertising comes with its own set of rules and goals.
At the end of the day, its about getting targetted traffic to a website and converting the acquired traffic into a positive, goal based result as efficiently as possible. Both PPC and SEO can do this when done correctly and coherently.