You are going in the right direction. You just need to add and adjust a few things.
Your declaring days as a variable twice, remove the var in front of the second days.
You're not getting the price because getField("days") does nothing, getField is undefined. Assuming your trying to get the input element's value by id:
var days = getField("days").value;
days = document.getElementById("days").value; // this gets you the input value
So your function works when i tested it.
If you want the user to see the price total. You need to add a dom element somewhere on your page to display the price total text.
Price Total: £ <span id="total">0</span>
Within your function, you would assign a new variable for the total, grab the page element, in this case, the span id, and change its innerHTML to the price. Also you may want to format the price value, as mentioned before by wbport.
SIDE NOTE: Notice how I'm using £ instead of £. You should be using the equivalent html entity of the pound symbol in your html, instead of typing pound key on your keyboard, for international compatibility. Or use a css font icon, like with font-awesome.