Take a dip into our Alladin's cave of parts.
We will call to discuss the details...
Put too much money in the honesty box and we can refund you.
Put too little in and you have to get your card out again (and we called you...) and we have to create more paperwork.
How much is too much?
Short answer £3, put £3 more in than you think.
Long answer: you are paying for the part, the bag, the stamp, the paperwork, & the legwork.