Disclaimer, I've never used share price, but I use Organization, Place, & Offer frequently.
Based on past usage of exitpoint Offer: I'm not sure it is the best fit. Offer is meant to "sell" as a Organization > (optional POS) > Place > (optional service/product/thing) > (optional reviewed entity) > Offer, whereas stock price is more like a "organization attribute" for an upper layer. True you are "selling parts of the company" but its not a tangible asset or a service that a company can sell like a service/product/entity is. No company is in business to sell parts of itself, ya know?
That being said, if it were me, I would approach thing as a thing - those are meant to be general enough to be injected as Organization in an upper layer of RDF.
If you are using this for a big company, get more info before blindy expirimenting. RDF errors can stick for 8+ months. I specc'd a couple traders, no RDF appears for share price. This could imply that engines hold them aside, preferring to use their own trade lookups. I havent seen any, but if you can find rich SERPS of any page in any major search engine that can display trade price/history, that would be the place to crawl using the Google Rich Snippet test.