The trip down from Havre de Grace to the open expanses of the Chesapeake is about 5 miles. Most days you can sail either down, or up the channel, depending upon the wind direction. There's a pretty good basin with fairly deep water in front of Havre de Grace, and sailboat races every Thursday evening throughout the summer months.
There are lots of marinas in this area, Tidewater being the largest with full services. The Tydings Park Marina is owned by the city of Havre de Grace, and the last time I checked there was a waiting list, but openings do come up once in a while. I'm in Perryville at Owens Marina and there are at least four marinas upriver from me. Prices vary from marina to marina, and most offer about the same commodities.
When my boat was at the Sailing Emporium at Rock Hall, the price was fairly high, and it was a pretty long trip to reach the bay's open waters, or at least it seemed that way. Worten Creek would be a good location, and there are at least three marinas there that provide sufficient depth for most sailing vessels.
In the North East River, you'll find Bay Boat Works, Jackson Marine, and several others located in the river's upper reaches. It's about 7 miles from the marina area down to the bay's open expanses. The channel width varies quite a bit and if you stray very far out of the channel you'll be stuck in the mud of the Susquehanna Flats. This area is just a short drive from Wilmington, though.
Good luck on your marina search,