Spin Bike help: Schwinn Evolution SR

The bike is as old as the hills but it serves its purpose in the torrential rain that we have had in the SE of England.  Being hard art hearing, the squeaking and noises from the bottom bracket can be ignored - but it is beginning to bug me.

It is not the front flywheel as that will spin quietly.

According to the Schwinn site the BB is an ISIS 1 7/8 inch diameter  BB (47.6 mm).  No mention of English or Italian thread - or shell width.  The Schwinn replacement ranges from 80 GBP to 125 GBP.  The OEM is made by Truvativ.  Does anyone  know of any other potential BB that will work?

Thanks