The price is going to depend if you just get the fan, or if you get the fan/heatsink assembly. HP Parts Surfer wants $65 for the whole assembly, P/N 680551-001. I also saw them online as refurbs for over $120. If you just get the fan itself, it's pretty cheap. Say, around $10 to $15. I think someone said they saw one online for $8. If you do go the new fan and/or heatsink route, can you do the work yourself or will you need to farm it out? That can increase the price quite a bit, depending on who is doing the work. Just like on your car.
Here's a video showing the disassembly of an HP G7-2000 series laptop, the cleaning/replacing of the thermal paste, and the removal/reinstallation of the cooling fan/heatsink assembly:
[ame]https://youtu.be/MoSrAPF_8fo[/ame]
Bear in mind that this video may not be specific to your exact model. There are some slight differences between the various models in the series. Just a heads up.
If this doesn't intimidate you, I'd say give it a try. You might find you only needed to clean your fan and heatsink and it works as good as new. Or, the fan might be okay but you just needed to redo your thermal paste.
Whatever you decide, however, is entirely up to you. It's your laptop. We can only make suggestions. Good luck!