The value really depends on the condition, not the year it was manufactured. Earlier ones will have milled floor plates. Later ones will have stamped floor plates. I've never noticed this to have a large impact on value either but I imagine the milled type would be preferred by most.

$300 seems to be a good average these days. You won't find many in decent condition for less than that. $400 is about the max for one that looks unissued unless it's a Mitchells collector grade, they price them around $500 but its still only worth what it's worth based on condition so I would never recommend paying Mitchells premium. You can find beat up ones for $200-$250 and really bad ones for $150 but there really aren't many really bad ones.