What is the difference between a $75 stereogram and a $7,500 stereogram?

$75
Text message only, no objects.
No revisions. All sales final.
Image size: 8 1/2" x 11" maximum
300 ppi (pixels per inch) high quality RGB digital image.
Includes a 72 ppi screen version (can be client specified.)
All rights reserved by the creating artist.

$7,500
Work with and accommodate client as much as possible
Any subject, style, and/or texts to clients specifications
Reasonable amount of revisions
Image Size: clients specifications within technical limits
Rights: distribution and copyrights as desired by client

Realistically, most jobs fall between $240 and $2,400

Custom work pricing varies for a lot of reasons. 
Specifications:

Is image to be "Hidden-Image" stereogram, or "Non-Hidden"?

Hidden-image stereogram: when the 3D image is completely hidden until viewed correctly.
Non-hidden-image: when objects are apparent, but appear flat until viewed correctly.

All images are met to be viewed with parallel vision (eye divergence)

RGB, or CMYK?
Size specifications; landscape, or portrait
File Format: usually JPEG, or TIFF
Images will be submitted as 300 ppi, CMYK, maximum quality JPEG's if not otherwise specified.

PRICING: All amounts in US dollars (USD):

Custom Work: Cost basis is $45 per hour.
A single image project usually falls between $450 and $1,100 for custom work. Multi-image discounts available. Factors affecting cost are:

Adding text may--or may not--add extra cost. (Text can be a very effective 3D element, and can be simple, or as complex as the primary image.)
Surrendering any, or all rights to an image adds extra cost.
Revisions: always create extra costs.
Degree of "print readiness" may add extra costs.
Size may--or may not--add extra costs.
A digital version for screen display is small extra cost.

Please Note: Payment by wire adds another $20.

Existing Images:
Use of stock images begins at $120 for one time use; all rights reserved by artist. A grayscale image-map (reveal) may add extra.

Cost add-ons:
Any further manipulation of image to client specification, including re-sizing, or addition of text.

Sending Images:
Images can be sent to client with email, FTP, or HTTP.  HTTP involves going to a URL, and clicking on a link which automatically downloads a .zip file of image/s.