C8 or C11 with Fastar. The C8 using Hyperstar with the Qhy8 camera has produced some amazing DSO shots. And the C8 is no slouch for Planet imaging either. The C11 of course would be better still. The C9.25 is an excellent choice also but does not have Fastar options, so you are limited to Long FL DSO work or at best at F6.3 using a reducer. But with this reducer you are limited to small CCD sensors only. A DSLR sized sensor would be affected by some Vignetting.
Note that long FL DSO work is not an easy thing to do, and is much more sensitive to the ability and quality of the Mount.
Get a used C8 with Fastar and also a GSO 8" F5 Newtonian for DSO work. You can then upgrade the C8 to a C9.25 or C11 when your budget allows.
A used C8 can be had for sub 1000. And a GSO 8" F5 should be about 300-400 new.
Have a look at this thread and the link I have provided for the TEC140 vs GSO comparison.
http://www.iceinspace.com.au/forum/s...d.php?p=327139
Regards
Fahim