For a good deal and convenient location check out The Francis Marion Hotel.  The Vendue Inn is also very nice but a bit pricier.  Some B&B's blocks from downtown can be reasonable but expect to walk more for dining and/or shopping.

The city is full of delightful places. I particularly like French Quarter Inn, a small boutique hotel in the center of the historic district but on a side street so the noise from city life doesn't filter through. Not sure of the pricing, but 0 George St is very special. If you want to be isolated and in a beautiful setting but about 20 minutes from city center is The Inn At Middleton Place is steeped in history and on the Ashley River. If you want to be at the beach, your best prices in your range would likely be Isle of Palms. As far as March, it is usually windy and very cool to cold so be prepared for that. Frankly, it is really hard to get a bad meal in Charleston. My two historic district faves are Slightly North of Broad and Cypress depending on what kind of experience you want, I like to just show up and sit at the bar and order. If you want a white tablecloth experience, make early reservations. These are a couple of suggestions, but I promise I could make 50 more that are just as good. Try Fish for early dinner at a great price, Stars and on and on. OH yes, a must do is Hominy Grill for real southern fare. OK, gotta stop, but you get my drift.

Pavilion Bar has a great view of the city and great atmosphere

The Gin Joint very unique drinks

Try the Andrew Pinckney Inn or the Vendue Inn, both in the historic district with reasonable rates and unique rooms.

I agree about the French Quarter Inn. Or the Market Pavilion Hotel.  Both superb.  For a different experience, try a B&B as there are many outstanding ones in Charleston.  Finding good food is like shooting fish in a barrel. . . many great choices on virtually every block.  If you can get in, try FIG.