ACOGs are worth the price, ill give you a link to a special list where you can often find em for pretty cheap, but look for deals because they are often overpriced by venfors
AFA the 6.8 SPC its an outstanding round up to about 400yds, it packs a punch and is a perfect intermediate cartridge and what we should switch to IMO
They are a little spendy but if I had the money thats what Id be going with.
Heres the link i mentioned above-
http://www.samplelist.com/
www.swfa.com has some good prices too. Id also look around at various auction sites etc; you can often find great deals, if you have an ArfCom account their EE is full of good stuff