The first field (let's say it's called Field1) needs to be a plain text field, set with the Number format.
Then you set the second field as a Number field as well, with the pound currency symbol, and this code as the Simplified Field Notation calculation:
Field1 * 750
For the second scenario just set the export value of the check-box to "250" (no currency symbol!) and use the built-in option under the Calculate tab to perform the total calculation, which is the sum of this check-box and the other field(s).
Thank you very much for your help.
I've got the calculation to work, however I can't get the second one to work. The calculation field only allows either "Value is the", or simplified field notation and not both?
You want to combine both things in a single field? Then you can use something like this as the Simplified Field Notation:
(Field1 * 750) + CheckBox1
Thank you again!