Lens Advice sigma super wide II 24mm f2.4

[samsnikon]

Hi

A friend is selling one of these , its old and comes with the front and end caps. Not boxed etc.

I have a couple of questions:

1. What is a good price for this lens
2. What do I need to check before buying and how do I check that

e.g. scratches on lens by looking but I have no idea how to check the blades etc or for fungus etc

thanks