Woot.com has a SIG 3x compact scope available for $95. I'd think that this should work for most PCPs. I don't think that it is specifically rated for springers though. Price is about 40% off the Amazon price of $160.
SIG Sauer CP1 Compact Prismatic Rifle Scope - Red/Green Illuminated
SIG Sauer CP1 Compact Prismatic Rifle Scope - Red/Green Illuminated