One of the Execution Only PRSA providers will allow you to keep your costs relatively low, such as prsa.ie (I have no link whatsoever to them). These should have no entry charges and a low management fee. I'm sure there are a number of threads already covering low cost pension options, but search for 'execution only PRSA. I haven't figured out yet how to link to another thread!
The downside of most 'execution only' and low cost PRSA's are that you are limited to a selection of the life assurance company funds and there is a fixed management fee, usually 0.75% - 1% for basic managed and equity funds. The Zurich PRSA seems to be the most popular with the low cost providers.
Depending on your fund value and investment requirements, a small self administered pension could also be an option. The costs are high to start with but it can save you a significant amount over the longer term, particularly if using ETF's, Direct investment and Deposits. Set up costs range from €1,000+VAT upwards, and trustee fees vary depending on the complexity of investments within your portfolio, but can be as low as 0.25%.