Shahinian Obelisk Passive Radiator Replacement

I just bought a pair of good condition Shahinian Obelisk speakers at a garage sale for $5 :-). Unfortunately, both 10" passive radiators had been completely removed and are gone. Shahinian Acoustics wants $275 for a replacement pair. Parts Express has replacements for $60 (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-494). There are also used pulls from good speakers on ebay for $25+ dollars.

My question is are passive radiators that sonically critical and precisely matched that I have to buy the $275 pair from Shahinian or could I get by with one of my other choices without muddling up the speakers? And if so which ones? Or are there other choices or vendors I should consider for the replacement? Thanks for the advice!!