Multiple Resized Photo Download Option for Photo Stores

Can someone please help me. I’ve looked around all over and grappling with various useless scripts for a photo selling website for over 6 months only to get disappointed everytime. This time i have decided to stick to wordpress and only wordpress.

I want to launch my photo-store in wordpress and i found wp estore plugin option suffices to a lot extent, well integrated with the nextgen gallery plugin.

Wp estore is rocking for selling digital downloads one off.
My problem is that i have thousands of photographs. And they need to be available for download in atleast 3-6 size options. Variations in terms of dimensions only. I mean that is how all photo selling websites are.

But currently the wp-estore plugin requires you to manually paste each variable urls, seperated by comma. and this is something beyond my capacity, specially when i have thousands of photographs and constantly growing because of contributing photographers. If there were a couple of hundreds and one time thing, i could have still managed. Resizing them and pasting each link separately.

I will take a lifetime doing even a few. Can someone please help me. I am frustrated.
I want when someone clicks on a photo he/she goes to the individual page and finds the available size variables set for that photo. (Don’t even need thumbnails)

Then on choosing he downloads the desired size automatically. Maybe getting resized while downloading or an option for automatic resizing when uploading photos with nextgen gallery. Thus the url destinations getting updated automatically.

If someone can help me with this little script to save my life, i will be a slave. thanks in advance