Do you have a digital camera? Then you can save yourself some hassle and money and take the passport photo yourself.
The guidelines for passport photos are available from the Passport Office at
http://www.dfa.ie/uploads/documents. /photograph%20guidelines.pdf.
As long as you follow the guidelines (a regular mistake is not having a neutral background) you'll be fine. Remember to take the photo portrait-style.
You can then get the photo printed passport-size through online sites like Spectra or regular photo developers.