[AtlUmpSteve]

I also strongly prefer TheArbiter. Pricing is actually based on the number of users and options; here's a look at my pricing screen.
Maximum Officials 80 0 $5.00
Sub-Assigners 1 0 $25.00
Payroll 1 0 $49.00
Check / 1099 0 0 $50.00
Evaluation 0 0 $99.00
Penalty Report 0 0 $99.00

I believe the max is $6 for up to 50, $5 for 51-99, then $4 for 100+. These are annual charges. Options include adding subassigners, payroll module, check writing and 1099 module, and evaluations. The key here is that being web-based, your officials can check the system from anywhere and anytime, update their calendar multiple times a day, if necessary. Sites have direct links to Mapquest. Your assignor can give varying levels of permissions to individuals, as he sees fit; some may be allowed to view their partners before accepting an assignment, board members can see the master schedule, some can be allowed to self-assign. Umpires can block individual sites, teams, or partners; the assignor can do those blocks without the umpire knowing that John refuses to work with him.

Even better, when you belong to multiple associations (even in different sports), it is impossible to double-book. Once one has assigned, you are blocked on other associations. When you block a date for personal reasons, it can block you in all (or just some) associations at once.

It is simply the best. And fairly intuitive to use; both for the umpires, and the assignors.