If you had a pc or laptop issue are those prices reasonable when new equip is getting cheaper and cheaper?
Who is your competition? What do they charge? What level of service do they provide for that charge?
What level of income do you need to support yourself and your family? Can you provide a quality service at a rate that competes well with similar services and still provide what you need to sustain yourself?
If a £50 flat rate fee is sufficient to cover your overheads (vehicle (including depreciation & maintenance), fuel, tools, training,
time), plus provide a high enough wage, and still beat what your competition charge then it sounds reasonable (what do PC World charge for making the customer take it to them? Over £60 IIRC.)
And if £40 covers your overheads (2x the fuel cost, vehicle, tools, training, work space, utilities, time) plus gives you a sufficient income then that sounds reasonable too.