I have found two not so pricey convolution reverbs:
SIR is freeware and the developer appearently contributed to the Wizooverb later. It uses mono impulse responses.
A stereo convolution reverb is ConvoBoy from www.elevayta.com . It has a freeware/donationware edition and one with more options for about USD 20.
A very useful thread about high quality IRs has been posted in this forum here: