Confusion with adding price to attributes

Hi site is http://www.fusionherbsorganics.com.au/

I would like to have products available in 2 formats
1)weight and I'm guessing I have to set this up in grams to be able to calculate 200g or 1.5kg?
2) per item, eg 6 bunches of celery, 4 paw paws

I have been looking at attributes as suggested to me in a previous thread and can understand assigning the option name and value but get confused with the price and how this calculates.

Shipping is not involved as shop owner delivers locally for a flat fee. I even wondered whether this is too complicated and whether I should just put the instructions in the product title. I know I've got myself a lot confused. I have changed the product quantity decimals to 2 and set the price to 0 and set product priced by attribute in the Product Master Category. Can attributes be used to calculate the price?

Customer needs to be able to put in their own weight or per item so this is a text field.

Appreciate any help. Thanks for all your help so far. Hopefully am getting to the end of this.