were both from Ireland and are planning on getting married on holiday at christmas
It’s just myself and my partner, were not having any guests, it’s just for the ceremony
You probably are asking about the wedding party, not the registration of the marriage certificate.
The cost of the wedding party depends on how many guests you will have and its location. 100 guests at a nice mid-range hotel in Bangkok would be around 100,000 baht. You can go much higher, of course, by booking it at a 5-star hotel and having many more guests. You can also go cheaper with fewer guests and catered at someone’s home.
On second thought, maybe you are asking about a western style wedding, meaning at a church with a priest and all that. Not sure about costs but there are a number of Catholic churches in Bangkok. The wedding party, i.e. reception, would be the same as I mentioned above.