How long is a piece of string?
This is quite an impossible question to answer. It depends so much on your taste. In Terms of Sheng - while there are some who like young Sheng, i don't. So i buy cakes of young Sheng, many in your price range, i store them for about ten years before i drink them, because i do not like young Sheng Pu Erh, i love aged Sheng.
I would look at another Shop as well - Yunnansourcing, run by Scott, an American who lives in Yunnan. He has a huge range of teas, and also produces his own cakes.
A Sheng that is not bad at all (i have 3 cakes), and is already quite drinkable, but slightly over your price range, i can definitely recommend:
http://www.yunnansourcing.com/store/pro ... oduct=1920
Next are two teas that are below your price range, which are due to slightly older raw material less brutal, but which i personally would store for several more years:
http://www.yunnansourcing.com/store/pro ... oduct=1867
http://www.yunnansourcing.com/store/pro ... oduct=2174
I can't help you with Shu because i don't like Shu.