Somehow I bent my rear derailleur hanger, how would one suggest bending it back into line? In my case the rear derailleur hanger forms part of the frame and therefore if I snap it when bending it back, I could write off the bike.
There is a tool specifically for this. For example, by Park Tools. Might that help?
As I said in comments, the real question here is: do it yourself or pay someone else. You can't really ride the bike as it is, so you don't have a lot to lose if it turns out to be unfixable.
A simpler approach if you don't want to buy the expensive tool just for this is to use something else to bend the hanger straight. I normally use a large adjustable wrench. Clamp it tightly to the hanger and twist cautiously. I'd do it in two or three movements, first the vertical alignment, then twisting it, then possibly re-doing the vertical. You will have to remove and re-fit the derailler a couple of times, and you will probably struggle to get it exactly right. But 8 speed isn't too sensitive (with 10 or 11 speed you're probably not going to get it accurate enough by eye to shift reliably).
An old m10x0.1 axle with nuts can also work if you have one. The important thing is that you have nuts or washers with a surface area as large as the flat on the hanger, because you really don't want to be twisting the hanger using the threads - that is likely to ovalise the hole and damage the threads. So you really need a cone and some washers, but ideally an m10x0.1 nut.
That bend isn't too bad IMO, it should be simple enough to get it working again. My main caution is that if you find yourself in your third round of bending it, give up and get someone with the right tool to do the job. Bending it back and forth is how you will break it off.