there is also a shop off dobin road, in that motor park type thing, i forget what they call it ow, but where the new gas station is accros from mobil and mcdonalds. Its teh shop on the end, you cant miss it. They do decent work. Not sure of prices as ive only dealt with them once, usually just go there to talk to them and go with my friends who know them.
Its called Audio Connection. If you are coming down on Dobbin Road from 175, you take the first right at the light and then the first left, and then its the first store on the right side. Its right near Fuddruckers and Starbucks.
As for the tweeter qoute, tell us what you told them to get done or what you want to get done. When i went there just for a quote, they quoted me $800 for fiberglassed boxes and an amp rack. You could really do it yourself. Just read up on here, buy some mdf, make a box, and install. As for the install, its really just running a fused power wire from the battery through some hole in your firewall to the amp, a ground wire from the amp to the chassis, a remote turn on wire from the headunit, and whatever speaker wires.
But if your willing to dish out the money, East Coast Car Toys has produced by far the best work that i have seen in the area. They are located in Annapolis. Westminister Speed and Sound is good too in terms of their installs and there in Westminister.