If you know what you're doing and you're good at programming you can use R. You might also be interested in contacting these guys to get some training:

http://www.cvent.com/events/decision-modeling-using-r/speakers-9a63b1fb68274f1391a3074792885ed1.aspx

yes you can use R https://sites.google.com/a/statistica.it/gianluca/bcea

or can do it in Excel (not free as such, but most people have it)

You can get trial version of TreeAge for 14 days for free and also has student version, you could buy for cheap.

http://www.treeage.com/trial-download/

Thank you for all your comments. I would like to use Excel but maybe R is a better option. TreeAge is too expensive (the free or student versions do not allow to save results and conduct a full cost-effectiveness analysis.

Any free excel spreadsheet I could download?