costs of a full blown Circuit Court action could be €15K if you win!! and more than double that if you lose. You will have to engage a lot of expert witnesses. If you win, you MIGHT be awarded costs against neighbour, but being awarded and collecting are two very different things. Even if awarded, you might have to pay your legal team and all the witnesses and then HOPE to collect against your neighbour. In theory if he does not pay (having lost) you can put a judgement mortgage on his land or even force a sale, but bear in mind the attitude of other neighbours/parishoners towards forced sale.
On the other hand, if you lose, he can do the same!