General guideline or article about selling web services?

Do some testing!

Go to fiverr.com or any freelancing site!

Hire any one you need to complete your first local business website for a sample!

Do your own part that you can do to minimize the cost!

Then break down any money you have spent on those freelancers! How much you've already spent to make it (the site) ready? Note it!

Don't forget to count your own work! How much do you want for your own part? Calculate this as well!

Then when you find out how much money is needed to create that sample site, you can mark it up for some profit as much as you want.

So, you will know how much you should sell it to your prospects/future clients.

There will be PROBLEMS...!!

You may need to do couple test to find out some people that you want to work with you from that freelancing site. You will be confuse selecting those people based on their performance, result quality, their fee, loyalty, and as well as their manner in the relationship you will build with them. Language is also a thing you want to consider as well.

So, by all mean... it's simply will cost you some!

For marketing approach:
Just do the same thing with people who offer their marketing ability in your niche!

Hope this helps.
Thanks.