One is a premier product, the other for the mass market. As ever a little extra performance, a little smaller footprint, additional functionality above the norm and above average build quality/fit & finish always add up to a signifiant increase in pricing.
The 7.7 most compelling feature is the hires Super AMOLED Plus display, the Tab 7.7 also has APT-X which delivers near wired performance over Bluetooth (compatible RX). If the $$$ are not an issue go with the 7.7 as it`s one of the nicest tablet`s on the market and best in class at present, if you are cost conscious go with the Tab 2, it will likely get the job done, the only cavet is if you try a 7.7 first your going to want that Tab to be the one in your hand...
I went with the 7.7 and will wait on ICS, it`s simply in a different league compared to other tablets, fast, sleek, looks and feels fantastic.