What are some amazing (and cheap) things to do in Ireland?

Me and three others are doing a little backpack trek in Ireland. While we're ok with doing some touristy things, we also want to get off the beaten track. Two of us are experienced riders, two are OK, we all want to ride in Ireland. We want to keep the price down, of course. Are there any riding programs near Dublin that would allow us to explore the Irish countryside on horseback--maybe even without a guide or at least with one who could allow us to be the experienced riders that we are?