Woocommerce price automatically change depending on quantity

General information for the website: We sell industrial packaging solutions
Kind of development: Customization of existing website
Description of requirements/features:

NEEDS TO BE DONE BY END OF TOMORROW 29TH JULY

There are around 20 products that need this doing to them.

What I want is something like this - http://www.packer-products.co.uk/RIB13W-mi.html - where the price per item changes depending on how much the customer orders. I know there are plugins which you can set discounts but I want to be able to set a fixed price.

I have already written the prices on the description of each product. See an example here - http://www.development.fromm-pack.co.uk/product/13mm-serrated-seal/ - I will need to be able to update the prices myself afterwards and add to new products when needed.

My budget is not fixed as I don't really know how much work goes into doing something like this but not looking to spend over £50 if possible, of course if you can show me you have done this before and have a full understanding I am willing to discuss budget.

If you have done something like this before please provide links for me to look at.
Extra notes: