That's really up to your local market. Use eBay for each piece in your location. Checkmark the option for sold items. Then you'll see what they sell for not what people are asking.
- If all you can find are US sales. You can likely get 15% to 20% more in other markets.
- eBay, Paypal and shipping will eat away about 20% of the value.
- CPU and motherboard should be sold together. To reduce return risk.
- Try selling locally first. eBay gives a good idea of value. Local sales means no fees and no returns. Plus sometimes idiots ruin good components. Due to lack of ability to install them properly.
- Big eBay sellers command higher prices. Don't go starry eyed at a few high priced sales. Look at the average sold price for a realistic sale price.