Tubes for Audible Illusions Modulus 3A?

I have an AI M3A from around 1995 that seems to eat tubes on a regular basis. I got it used in an A-Gon purchase,it had stock Sovtek tubes,which were clearly past their prime. I've since tried some Electro-Harmonix 6922's,which developed noise very quickly,some Golden Dragon 6DJ8's which lasted a bit longer,but now one is hissing away in the left channel. Should I bite the bullet and pay AI's ridiculous price of 35.00 per tube,or has anyone had good experiences with alternatives for less money? Thanks. Bob LaBarca