You can only select the amount of images that you have points to process. If it will only let you select 192 images you probably only have 770-ish points in your account (assuming a 20 megapixel camera).
The size of the imagery in megabytes does not matter in the pricing. We charge by the megaPIXEL of imagery. 1 point is enough to process 5 megapixels.
If you have scaled the images it may be calculating the points incorrectly depending on how you scaled them. You can email a couple of samples to email@example.com for review.
This site is separate from mapsmadeeasy.com (note the URL at the top) so it requires a different login credential.