Hi all,
A site allows users to post text. I'd like to know how to go about charging a small fee to post additional stuff, say for example an image(I don't actually want to charge for an image, I merely use this as an example).

I have a vague idea but I'd appreciate some fleshing out.

Let's suppose I have an 'input text' page. This allows users to post text free of charge.

Some users then want to add an image. At this stage I assume they need to click a 'pay now' type button and are then directed to paypal. After making their payment they are directed to an 'input text plus image' page, where the facility to upload image exists.
On submit, image and original text(which has been stored in a session) are uploaded.

Does this sound about right.
How do I ensure only users coming from paypal, have access to the 'input text plus image' page.

Any help would be much appreciated, even if it's directing me to a suitable tutorial.