IBM lowered support prices and changed their support policy for Geronimo based application server - Websphere CE. Instead of charging per core, new prices are per socket now. Two support options are available - Entry and Elite support see difference. Entry support is 1030 USD per year and Elite support is 3500 USD per year. Elite support includes phone support and 5 developer support incidents. Yes, they can help you with writing your application!
Oracle has Glassfish application server, which also competes with Community edition of Websphere. You can find pricing in Oracle online shop and as you can expect its kinda expensive for open source software - It costs 5000 USD for base software and 1100 for 1 year of support. First year will cost you 6100 USD, but next years just 1100 USD, etc. It is licensed per processor, which means that 1 dual core intel cpu equals to 1 processor license. If you have more CPU cores - servers usually have 4 or more cores today you need to buy more licenses.
There is also Resin application server which costs $699 per CPU, but I don't trust that company. They have really badly designed website and its often inaccessible. Their server is not certified as J2EE anyway. They have some big customers and they were mentioned in Gartner magic quadrant 2009 report.
Websphere CE - cheapest J2EE application server