Got some more info.
After your initial purchase and 400 included locates/ping/exchanges, the following year you have this option:

xchanges / cost per year
150 /$23.40
400 /$59.50
1000 / $139.95

That 1000 exchanges comes out to about $7/month!!!!!

There are other options for those who need to keep track of their vehicle every minute.
Exchanges can go up as high as 1200/2500/5000 (unlimited). With 5000 exchanges, it's still only $19.95/month (paid yearly).