How do I avoid duplicate content penalties for this idea?

I have a set of keywords with an associated affiliate that's new to the market. The keywords are pretty much an open field, with less than 10,000 SEOC in Market Samurai for all of them, and some as low as 2,000, with 30-100 searches per day for each.

The pattern is like this: "<state> <keyword>". For instance, if my keyword was "tanning bed bulbs" (it's not!), I'd be targeting "Arizona tanning bed bulbs", "Alaska tanning bed bulbs", "Arkansas tanning bed bulbs" - etc.

I know how to dynamically generate content for each of these pages, and map the URL to the the right parameters on the script - no problem. My problem, though, is that if each sales page has the same content with the exception of the state names, I'm quite sure that Google will flag it as duplicate content and my site's pages will be impossible to rank.

I can include in the script a basic spinner that would output a randomly hand-spun sales page, and that might work okay, but it would serve different content each time - and probably seriously harm my on-page SEO in the process.

To take it a step beyond, I could use the spinner script to save a set of parameters that output the same page each time the state's page is called - but would that necessarily be better?

Finally, how much can I repeat from page to page before Google starts to discredit me? A sentence? two? A paragraph?

I'm really not trying to game the system here - the service I'm advertising has state-specific offers, and the link will be customized the individual state. People search for this stuff particular to their state, and I'm going to help provide it. I just can't figure out a way to do it that's not going to get me sandboxed.