Can I dread my hair by myself?
Yes you can! It's a little difficult, well I'd say it's more than a little difficult, but it's done quite a bit and you can do it too.
Here are some helpful tips:
Having someone braid your hair in the sections you want will be cheap and easy. Then only the backcombing remains. This can save you A LOT of time coordinating two mirrors while trying to keep your arms above your head while every ounce of blood drains out of your arms.
You might try holding your hands above your head and rubbing them together for ten minutes straight - this will give you a good idea what you're getting into before hand.
Always, give some real effort to finding help before you decide to go solo.
If you're having trouble finding someone to dread your hair, give some thought to doing everything you can reach and see and then just beg someone to finish the back. If 3/4 of your hair is already dreaded the back really doesn't seem like much. Combine this with having your sections done and held with braids ahead of time and things will be much more manageable.