Develop a Mac and PC Application

I would like a local database application made which works on both Mac and PC. The application has to look really professional like most modern Mac software applications are. The idea behind this application is that it allows an agent to keep track of buyers (on one side) and sellers (on the other side) and it allows him to make connections between the 2 sides. See the attached image to see a rough layout which I have imagined. The top of the application will contain menu items with buttons and icons and and search box and tabs and dropdown box. The left side will display a list of suppliers. The right side will display a list of buyers. The middle area will be empty unless a connection is made between a buyer and seller. If a connection is made, then the middle are will show text and relevant files. To make a connection between buyer and seller, a line will have to be pulled from a buyer’s box to a supplier(s). Once that connection is made, that buyer will be associated with that supplier (or suppliers). The boxes themselves need to behave in a certain way. By clicking a down-arrow on the box, it will expand and show additional details. By double clicking a box, it will move automatically to the top of the list and so will its associated box(es) on the other side and then the middle text area will appear ready for text writing/pasting. In each box, there is a visible area (default) and a invisible area which can be opened up and seen when the down arrow is pressed. In the visible portion at the top, the user can enter various bits of information. Initially, he will see text boxes for each bit of info. When he is done entering the information, they will become like labels (no text box behind it). While editing, if the user presses Shift+Enter, the text box will create another line below it for more entry. Thus, the visible area will get bigger and bigger depending on how many extra rows were created. The application will make extensive use of copying from another application (like email) and pasting it into one of the fields with the use of a right click menu. So you have to develop a right click menu (system wide) that will work. In the right click menu, I can choose to paste the highlighted text into a selection of fields on the active box on the application. On the menu bar, there will be a dropdown box where the user can enter the name of a product, and then see the entered products in that same list. When a product is selected, then the buyers and sellers associated with that product will be displayed below. Of course, there are many small items not mention but the application has to be made functional and fully without having to detail every small small item. If you can do this at a low cost, then let me know. Sky: webkept