who owns www.irena.com?
How can I purchase it?
How much will it cost?

The domain IRENA.com has already been registered by another individual
or company.  It will therefore be their decision whether the domain
name is for sale or not and the best way to find this out would be to
contact them directly.

As the domain name is a person's name I would value this domain to
have a /minimum/ value of US$750-1000.  Domain names of this type are
very sought after...

By doing a WHOIS search on irena.com you can discover who owns the
domain name and who the administrative contact is for this domain
name.

A whois search can be performed here (simply type in irena.com in the
box and press search):
http://www.networksolutions.com/en_US/whois/index.jhtml

The information I have tracked down for you is this:

Registrant/Owner:
Ultimate Search
GPO Box 7862
Central HK
HK

Administrative/Billing/Technical Contact:
Ultimate Search
GPO Box 7862
Central
Central, HK
0000
Phone: 25379677
email: dns@ultsearch.com

It appears from this information that Irena.com is owned by the
Ultimate Search company (sometimes known as someone called Yun Ye). 
Unfortunately this company is a company that owns a large number of
desirable domain names and is notorious in this area of domain
squatting:

http://www.expiredtraffic.com/index.php?page=ultsearch
http://216.239.59.104/search?q=cache:joIuojK6GLIJ:ultimatesearch.thecap.org/+%22ultimate+search%22+ultsearch.com&hl=en
http://www.namepros.com/archive/topic/27244.html
http://www.sitepoint.com/article/expired-domain-traffic/3

Judging by this information it would probably be easier to buy a
different domain name :-)  Some cheaper alternatives would be
irena.name, irena.us etc.

I hope this information is sufficient for you and good luck in
purchasing the domain name you wish.

Please thank your researcher for me.

Thanks