Shipping charge auto adjust? Upsale message?

Hi, I'm on 1.3.9h and I need something for my cart so obvious that I can't believe no-one mentioned it on the forum before, but I searched thoroughly and nothing came up.

First, I've successfully set up "free shipping for purchases over $20, otherwise $3 shipping fee". That was easy. Example:

order: $25 - free shipping, totals $25
order: $10 - shipping fee $3, totals $13

What I'd really like is this:

order: $10.00 - shipping fee $3.00, totals $13
order: $18.00 - shipping fee $2.00, totals $20
order: $19.95 - shipping fee $0.05, totals $20
order: $25.00 - shipping fee $0.00, totals $25

So that the shipping fee is dynamic towards zero when the free shipping limit is approached. Anybody done this yet?

In a related thought, I'd like to advertise the "free shipping for purchases over $xxx" feature, on the cart page, and in the cart sidebox, like

  cart: $12
  Add more purchases for $8 to your cart to obtain free shipping.

I'm capable of writing a few lines of PHP, but, to not reinvent the wheel, has anybody done this?

Any input is greatly appreciated!

For the second question:

http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=394

I haven't used it.

For your shipping, you might look at the Table Rate table shipping module ...

Then, for the Free Shipping, so that it stands out more, go to the Modules ... Order Total ... Shipping ot_shipping and enable the Free Shipping and set to 20.00 ...