I would say at this stage they would probably be best off kept hold of, as prices are likely to increase in the forseable future. The sale value for these cards varies, the Machamp for example worth slightly less (despite the 1st edition symbol) as it was sold in the starter theme deck nearly everyone had - and the Ancient mew worth more as is more sought after. The rest are really subject to their conditon. Cards that have less scratches and marks can expect a higher premium than those that have been played and scratched etc. A specific amount is difficult due to the variations in condition etc.