The numbers you see for pool totals are total dollars, not tickets.
A $1,000 exacta pool is a bit small, and can create some substantial over/underlays.
Tris are a little better. Though there are 6x as many tri combos as exacta, many are near-impossible longshots, so the $5,000 pool still can give a reasonable performance on the 'standard' finishes.
I wouldn't bet anything more than about 250 to 1, because you're goin' to meet the tax man if you win, and the pool isn't big enough to give a true payout on a big longshot.
Even if you hit the big longshot, you'll still have to share too small a payout with the box bettors.