Historically I have put 500-700 in brackets at nationals because I felt I had a 75% chance of making money in that field. Local tournaments, if I enter the tournament, which I always do in scratch events, I often don't max out the brackets. Partly if we are on a house shot I consider it more of a crap shoot, and unlike nationals the real money is in the regular prize fund.
As a side note, it is much harder to make good money in nationals brackets than it was a few years ago. Also as a 68 year old guy, I am usually more interested in the senior side. The interesting thing is that it is often as tough to make money in senior brackets as in regular. Also, the low cash score in the senior singles and all events has been higher the last two seasons than in the regular division in Reno. I didn't bowl El Paso, so not sure about it