Hi, Tarek. Auctions4Charity is an attractive-looking domain in the best extension. It falls into the brandable category--meaning that people will have to learn about a website with that name before they begin typing its name into search engines. The best domain in this area would probably be CharityAuctions{dot}com, since it is definitive, memorable, and people already type "charity auctions" into Google. You should look up CharityAuctions{dot}com at DNSalePrice.com and Namebio.com--2 sites that track some past domain sales. You may or may not find something. Whatever CharityAuctions{dot}com is worth, Auctions4Charity{dot}com is worth less. I'm personally a fan of the "4" because it's easier to read than "auctionsforcharity", but the counterargument is that some people DO search for "auctions for charity"--whereas nobody searches for "4".
If I had to pull a number out of thin air for your domain, I'd probably say $200 to $1000. That's what I'd expect an end user at Sedo to be willing to pay ASSUMING they come along. They might not come along for a very long time, if ever, you understand. It's a game of playing the odds. If you tried to sell on your own schedule or to other domainers, you wouldn't get as much as $200.