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It depends on the industry. If have concerns about spending the money, you may just want to submit to the free search engines (major engines)and see how it goes before you commit. This approach would also buy you some time to study Yahoo as much as you will need to if you want to get a top spot there in a competitive category.
As far as exclamation points are concerned, I wouldn't bother for a few reasons. Just concentrate on making your site valuable to your visitors and keep asking all the great people here for tips as you go.