The 300's are/were good bikes. Condition means a lot. A "couple hundred" dollar bike could cost a lot more if it's in poor condition. What condition are the tires, chain/sprockets, engine compression?
The 300's were first produced in either the late 80's or the early 90's. My 95 was the second one I owned, and my 09 is my current one. The engines have been redesigned several times since their first production. IIRC, from about 2003 onward, the engines are still pretty similar and share the same bottom end as the 250's. E start was added in 2008.