Argos are clearing out their PSP-E1000s for just under £50. With the PSP discontinued, this is probably the last chance to pick one up brand new - not even Amazon are stocking these anymore.
Note that this is the revised budget model released in 2011, with no WiFi and only one speaker. Any games purchased off of PSN can be transferred via USB cable from a PS3 or PC.
Probably the best platform for emulation when it's hacked.