My Dog is Having Pooping Issues!

[Tricky]

Poor Cosmo, my 8 year old Aussie seems to be having a really hard time defecating lately..
He strains and strains and only a little bit of poop will come out after all that!
Last Saturday I noticed some fresh blood around his anus.
I called the vet immediatly and they didn't seem to worrried about it.
He is eating and drinking fine.
Seems fine otherwise.
His belly isn't distended or sore to the touch.
I haven't seen any more blood since the one time over the weekend.
He just seems to have a real problem pooping!
I'm taking him to the vet this evening and I'm so worried this will be an expensive visit!
I just spent $500 on him last month when he hurt his neck and we had to rush him to emergency! (his neck seems great now)
Any info would be greatly appreciated! I'm so worried!
Thanks in Advance! Peace, K