The PCP's look great and I can get high pressure air but they are out of my price range.  What I would really like to find is a used parts gun that I can fix but those arnt turning up like I had hoped.  It looks like co2 is going to be the current option and I can just hope to upgrade it later on.  I have seen where some people have done that with the 2250 too.  I have old CO2 tanks and nitrogen tanks from my paintball days so at some point that my be the more cost effective way to go.  This is where I get confused on the models.  I have seen what I thought was a 2250 and it had a tank screwed into the back but I thought they used a co2 cartridge from the front.  I see the crosman site has a 2400 model but many of the modifications people are talking about are fro the 22** series.  Are they close enough not to matter or is the 2400 better to begin with?  

So what do yall think I should go with for modification potential and an accurate/ fun rifle?  Where are some good places to pick up used or broken guns as well as a new one?  I saw pyramid air come up a few times in posts but didnt see the 2250 on their site. For plinking and pest control should I go with .177 or .22 cal?