The information you need in order to evaluate the unit is:
1. How old is the RO membrane(90 GPD not 96 as Spectrapure does not sell a 96 GPD) , how long has it been out of service and if it has not been used in a while was it always stored with water inside it to keep the membrane viable? If it is say 2.5 years old or older or if it has been allowed to dry out it is probably due for a new membrane soon so factor that cost in.
2. Did they use high quality prefilters and solid carbon blocks from Spectrapure or other reputable vendor or were they something from Home Depot or a less reputable vendor on e-bay? The quality of filters varies greatly and has a direct bearing on the life of the RO membrane. Cheap filters pass more contaminates on the the membrane and cause it to wear out or fail sooner. Spectrapure is the only vendor I am aware of that uses absolute rated prefilters which is as good as they get. Visit their vendors forum here to read about the differences.
3. What DI cartridges are they, how old are they, how much water has passed through them and at what TDS? Spectrapure has some of the very best DI cartridges in the world, they are hand packed in layers using blends of resins they keep secret, but they work great. If the cartridges are old though or again have been allowed to dry out they are worthless and costly to replace.
I am still of the opinion if the unit has just recently been pulled out of service, its not too old and it has been maintained as recommended its a steal at $100. The quality of the housings and associated hardware in a Spectrapure unit are top notch and are almost worth the $100 by themselves especially if it has things like a pressure gauge, TDS meter or water quality monitor, bypass valve and autoshutoff valve.