Fungus typically looks like a random spider web or "tree" that is faint white growing from a single point. Here's an explanation.
Fungi in Photographic Lens
So I had a lens cleaned from fungus and the cost was $150.00. The shop did a great job and told me they have to clean the entire lens because the spores could be anywhere inside the unit.
Separation is another issue. Lens groups inside the lens barrel are cemented together. They are air tight between the pieces of glass. The cement somehow comes loose (being dropped?) and air gets between the glass elements. So the lens must be disassembled and reglued then properly aligned. It's only a job for a factory service tech in most cases and will cost more. My bet? $300 Factory repairs ain't cheap. I had a 2 hour repair done by Sigma a couple of months ago that cost me $450.00
So I recommend you get the lens to a service shop in the area and have them assess and give you a ballpark idea of fungus cleaning if it's that. If they say it's separation, then either get a refund or a big discount and live with it till it starts failing and you want to spend the money to repair.