You should be able to buy commuter tickets for NJ Transit (see http://www.,njtransit.com). Both Rail and bus you can purchase 10-trip weekly tickets at a substantial discount... usually approaching 50%.

Driving in really sucks. If you head in any time after about 7:15-7:30 figure at least one hour - sometimes 2. If you leave at 6 you should have no issues. If you drive in, pick an area away from midtown, near the subway and near someplace you want to go. If you're going to go in every day for 21 days, see if they'll give you a monthly rate. If you have an area in mind, I'm sure someone here can find a garage for you. Typically they're much less away from midtown.

You may also want to consider finding someplace to park near one of the Path stations - I used to do this in Harrison, many years ago (about 10 min from your hotel).