Employee Stock Purchase Plans (ESPPs) were heavily neutered by U.S. tax laws a few years ago, and many companies have cut them way back. While discounts of 15% were common a decade ago, now a company can only offer negligible discounts of 5% or less (tax free), and you can just as easily get that from fluctuations in the market.
These are the features to look for to determine if the ESPP is even worth the effort:
- Lookback Windows where you pay the lower price of either the start or end of the period
- Larger discounts than 5% (your company will be paying extra taxes)
- Short purchase periods of 3 months or less.
As for a cash value, if a plan has at least one of those features, (and you believe the stock has real long term value), you still have to determine how much of your money you can afford to divert into stock. If the discount is 5%, the company is paying you an extra 5% on the money you put into the plan.