How much is this worth?

1. List it for auction here or on ebay with no reserve
2. Describe the condition as "unknown"
3. Its worth will be defined by the market (Econ 101)
4. Send me 10% as a consulting fee

Sell it for the same price as the one you ''picked it up for'' since your question shows strong signs that you do not know much about turntables, and therefore you are probably unable to identify current problems that may be present and that could be passed on to the next buyer.

Not much good advice you may think, but an ethical choice for sure.

in good working and appearance condition, complete with arm, cartidge and cover, about $300 to $500

Any piece of gear is impossible to value without knowing the condition and seeing detailed photos. You don't even mention whether it is in good working condition.