Costs for window and skylight replacement range from $500-$1000 per piece with higher end ones costing more. You get what you pay for though with energy efficiency. You will see an immediate result in your energy bills even if it takes time to make-up upfront costs.
NFRC attaches labels for the energy performance of items. To qualify, you need this and U-factors and SHGC scores of 0.30 or less. These measure heat prevention and heat blockages from the sun. You must also owe more in federal taxes than you’re claiming in credit. Credit is $1500 and can be spread throughout the year for a variety of energy-saving upgrades.