I would suggest something with variable power, especially if you plan on hunting. Based on the max range you listed (300 yds) I would say 10-14x magnification max. Some people may think that is even too much, but I tend to like more magnification - increases my confidence to have a bigger sight picture. You don't need a 30mm maintube scope based on the range you intend to shoot, either, so that will save you some money. I have heard a lot of good feedback on Bushnell Elite scopes and I think they run around $300 or less. I personally have experience with the Cabelas Alaskan Guide scopes and I was extremely surprised with the clarity, low light capability, and ruggedness of the scope I had. They have a 3-12x52 30 mm maintube model that they sell for $350 I think and it is well worth the money. I now use Leupold scopes and a Zeiss Conquest and they are all excellent scopes, but the Zeiss was almost $600 and the Leupolds were $800+ each.
Also, plan on getting some decent mounts. It looks like you could get away with Medium rings with the spacer you have. I like Badger, but they are $125 per set. If you want quick release, the ARMS #22 rings are well made, and I have heard good things about Warne rings. You can spend as little as $30 on inexpensive rings or as much as $200 on titanium "uber-rings". I would suggest not skimping as the rings can be a weak link in the chain.
Hope that helps.