All stitch guides will list the materials you need but not all have stitch diagrams. Most will diagram unusual stitches but not the basics like tent stitches. Some will list the stitches and tell you what page they are located on in this or that book. Julia Snyder usually works this way, for example, referring folks to page X in this or that book she's written. The most famous stitch guide writers may charge more but not have elaborate guides. You are buying their expertise.
To help answer this question, I have collected guides for you to look at or read about in the links below. Note that some stitch guides have photos of the finished piece but many do not. A great many stitch guide writers don't have the time to stitch each piece they have done a guide for. They are using their experience to pick stitches without having the time to try them out.
I suggest you look at stitched models of all sorts of pieces, trying to find a style that matches your own leanings. That way you will be working with someone whose tastes are a bit like yours.
First up, a review of Amy Bunger's stitch guides and a brief explanation on why you can't buy them without buying the canvas and/or thread kit with the guide.
Amy's also written a bit about stitch guides in this August 2018 newsletter for her shop.
Here is a review of one of Beverly Churchill's guides for Melissa Shirley's Vintage Pears canvas, a classic design with a classic treatment.
Here is a review I did of one of Robin King's stitch guides.
Needlepoint.com also did a review of some of Robin's guides.
Associated Talents offers free stitch guides on their website for many of their smaller ornaments. The guides aren't very long or detailed but the end result is fabulous!
CBK also has some free stitch guides on their website for some of their many canvases. These vary in style and layout because they are from a lot of different stitch guide writers.
Palma Seljan has also created quite a few free stitch guides. Some have been posted here and some are available at Needlepoint Nation group on Facebook in the Files section. Palma's guides are very basic: a table that says use this stitch and thread in this spot.
Here's a basic free guide for a small Melissa Shirley Halloween "cracker" design by Palma Seljan.
Louise's Needlepoint has a nice article here about various types of stitch guides and what their shop guides are like.
Pricing varies from $5-$150 usually but custom guides cost more since they are priced according to the hours involved or the number of pages. Hopefully this answers some of your questions.