As for 70-200mm...Canon F4, i think new set around 1Kplus (not sure after price hike). Second hand is around 850.
Nikon, 70-200. Trinity you mean ? Cost heaven...Probably try to look at the older 80-200mm...Second hand (not sure if they continue this line) is around 1000.
Don't really bother with dust for body preference, if you know how to keep your gears properly and especially during changing of lens. It can be minimize.
You mention that you likes to take portrait but then why do you need to take it at high ISO ? If I am taking a candid portrait i usually stay at around 400. If it is more serious, i drop it into 100. That's my 2 cents =)