71mm refractor + barlow + deep sky = disaster. You really don't want to image deep sky (especially with a DSLR) at F10. Go the Vixen 8" F4.
I believe the Vixen is very solid and doesn't require as frequent collimation as the cheaper versions. Or a Bintel/GSO/Skywatcher F4 or F5 Newt if you want to do it cheaper and have money left over for accessories, as Rusty mentioned.
I'm having a blast with my Bintel 8" F4 for deep sky. My 100mm F9 refractor has been retired to Sun, Moon and planets, where it is more suited.