How did Charlie Sheen top the romantic seven-day getaway he just enjoyed with girlfriend Brooke Mueller, 29, at the Four Seasons in Costa Rica?

With a $500,000 engagement ring. Sources close to the couple (who were introduced by actress Rebecca Gayheart at a Victoria’s Secret party in 2006), say they weren’t surprised that Sheen and Mueller decided to take the leap.

“The two bring out the best in each other,” a pal of the Two and a Half Men star, 41, tells Us. “Brooke is a good influence on him.”

And the real estate investor is clearly doing her best to fit into his family, even shopping with his ex Denise Richards and their daughter Sam, 3.

Says a witness of the trip: “You could tell they were bonding over Charlie and Sam.”