Financial talk

Told him how loud my computer was since i've been dusting it, and he said it's the fan wearing out and it's best to get a new one, i asked how much it costed, and he said £10 for the fan and £10 for them to insert it, but its £35 to hire a tech to come out and fix it, and i haven't got that kind of money for them to do. My dad won't let me do it, so i need to do it in secret because if i don't do it, it sounds as if it's going to blow up and i'd like it to be sorted before it does, I have no experience in doing this, I'd pay for a new fan no problem, but i need my dad to drop the hard-drive down the shop for me, how can i bring up the subject? Okay, it may not sound a big deal to you, but trust me, with my dad, it's a HUGE deal. Thanks