A skilled machinist doing non standard work (not a semi skilled machine operator) will be paid £15 an hour or so. The employer has to add employers NI, statutory pension contributions and other odd bits so the person costs close to £20 an hour. Then you have to add premises, rent rates and power, machines (depreciation, repair), finance costs, tooling cos it wears out, employer liability insurance, many more small things, allow for the fact that you are not producing 100% of the time, management, quality control, selling time, admin like invoicing, put 20% vat on top of whatever you charge then make a profit.
£45 is pretty much the minimum.
Anyway, how square do you need square to be? If you need tight tolerances a file might not do it unless you are very skilled and very careful.