Update price via TEXT Attribute

We're trying to sell gift cards that can be of any value, It's an actual card that is loaded with the amount the customer requested and then mailed.

This is what I tried:
Set up Gift Certificates per the FAQ
Add Value as a TEXT attribute

Now when someone enters an amount in the Value field, the total doesn't adjust, which means the way I was trying to set it up is wrong (my guess is a text attribute is treated as a string and as such isn't added to the total).

Questions:
Is there any way to set up the gift certificate where a customer can type in an amount and have that amount update the total?

Or is there any way to set up a physical product where the customer can set its price? (sounds odd but that's exactly what a gift card is)

Or can I make changes to the code to have the text attribute update the total? (least preferred option)

Either way will work in this situation.

Thanks in advance,
Trini

Additional Info:
The gift card is the only product we plan to sell online.
Zen-Cart version: 1.3.8a/v1.3.8 new install

Make a Product ...

Set the Price to $1.00 ...

Set the Model to: GIFTcustom (anything you want providing it starts with: GIFT) ...

Look at the products_id ... let's say it is products_id 27 ...

Customize your template that when the products_id is 27 that the Add to Cart: uses different text and reads: How Much?

That is brilliant! Thanks!