SEO is worth the extra business that is able to be generated based on being on the front page of Google. No point being #1 if it generates no extra business. If it generates $1 million in extra revenue, then $50,000 would be money well spent as a marketing expense.
To aajvcad's previous comment, $3500 a month would be cheap in some industries, but on the low end of $690 mentioned, this is way above what some local businesses need to pay.
FOR EXAMPLE - one of my customer sites
Twin City Mowing Services is #1 for virtually everything everything he wants to be, and in the top few for anything that isn't #1. But his target phrases are "lawn mowing albury", "lawn mowing lavington", "lawn mowing thurgoona", "garden care albury" etc. With a limited geographical area and low competition, there was only a couple hundred dollars in
SEO work (beyond the website website development costs) and it pretty much sits there at number 1 with minimal ongoing link building.
To a business like this one my service was brilliant value. If he needed to pay $690 a month - it would be completely uneconomical for him as he is really only looking for a few new clients a month to be successful.
For anyone who care's reference, my services for
SEO start at $150 per month with a minimum 3 months for low competition locally based phrases. But I was asked to quote on something like "mortgages" or "real estate" I think I would just put a 1 and the hold down the 0 key for a couple minutes to give me a figure! lol
Matt