You should also try your physics and chemistry departments as they might get LN2 more often.
You also need to factor in the price of a proper thermometer to read down to -200C, try search amazon for j-type thermometer, as most all of those will go down as low as you need and take both K and J type, but in the end you want a k-type probe. You also want good probes, most don't read down to -196, lol i have some crappy ones that only read to -170C lol.
Also LN2, did you ask about the dewar rental? Or if you can rent one?
IMO $2.5 per liter isn't bad but it isn't good. I go through like 25L in a weekend, and i usually run out, this is with ivy bridge. If you have a pot with a very reactive base, you will use less LN2. However if your pot is very thick, then you will use a lot. If your CPU has a CB you will use a lot, if it has a very large distance between your CB and CBB then you will use a crap load. I would estimate your first time you wont use more than 20L, but still that is almost $50, not even with rental of the dewar. I pay $35 for 25L, I pay $25 to rent a 25L dewar for 1 month( normal price is $150 + deposit, but I have an account with them now, so its nothing). Some places will allow you to take the dewar for a few days while you use it. I have been doing a crap load of beta testing and benching over the past 4 months, I have spent about $600 over these past months.
Sure you buy a pot for $250, your thermometer(BTW this one is good: http://www.amazon.com/Thermocouple-Probe-Thermometer-Channel-Scientific/dp/B001EUB6BM
) Recently I went to a bench thingy where I benched with the best OCers, and they basically liked one thing of equipment I had, my thermometer. Between us were about 6 thermometers, and the others IMO looked bigger and nicer than mine, but mine was the fastest. That becomes important b/c a lot of these thermometers take a while to change their temp reading, however mine just changes very often, its polling rate is pretty high. Plus it is $88 new and that is pretty good, it comes with 2 probes. Even in TW probes cost like $20 american(they also read down to -196, certain brand you can buy).
Also get yourself some of this, don't really mess with anything else: http://www.gelidsolutions.com/products/index.php?lid=1&cid=3&id=42
it is a very good paste for very low temperatures, and I think they have something new coming out too.
You will also need a torch(I use propane, but MAAP is hotter.) Propane head from homedepot is $25 and it comes with a free propane tank. Replacement tanks are $3. The torch will save you SO MUCH TIME!!!!!!!!!!!!!!!!!!!!!! Forget a heat gun, but then again i use a heatgun to dry stuff and melt SMD components off motherboards, this one is great: http://www.homedepot.com/h_d1/N-5yc1v/R-202102620/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=heat+gun&storeId=10051
IMO Cascade will keep you yearning for LN2, especially if you bench a CPU without a CB. Plus cascades don't exactly fit in nice places lol, there is also the chance of it breaking down. IMO if you want to bench do LN2 if it is possible. Also don't worry, it isn't that dangerous.