Hi Cassp
It seems you have a Yamaha keyboard? If so, I'm thinking you won't like the sound in mono which is what that Behringer is. I had looked at the PMH880S in stereo by them, only 19 pounds.
But, if you are considering the Peavey PR, why not get the new powered version. I know the 12's are only 35 pounds. That's only 5 pounds more than the old non-powered version. I imagine there is still some old stock floating around out there where they are heavier. I would definitely make sure it's one of the knew ones. Neo something or other.
That way even if something didn't work right, you'd always have at least one speaker to finish a job, whereas if using a powered mixer and it doesn't work right, you have zero speakers for the night.
Then you could pick up a Behringer UB802 non-powered mixer in stereo. Small, light, inexpensive, $42.00. If you want effects like reverb, Behringer has that and I understand the Alesis is another good choice.
For me, if I ever chose the PR sereies I would go the 12', mostly because even though the 15's are rather lightweight, the are as big as a refrigerator
I think also that the new Behringer lightweight speakers may be a good choice if you are leaning in this direction.
Best
Scott
http://ScottLMusic.com