my 2 cents - if it has a belt it is a 15-90, if there is no belt and gear driven it is a 15-91. Definitely a great machine and superb for FMQ! I would think if the "sewing related items" are decent (I am presuming that they mean attachments) that $75.00 with a decent cabinet is a fair price as long as they machine itself is in good to best condition.
I have a 15-90 and it is a great machine!
J