My choice would be:
St Paul Co-ed > St Joe > St Paul Boys
Unless you have connection with St Joe, it will be too risky to give up St Paul Co-ed / St Paul boys to go for the lucky draw (about 80% chance ending up with nothing good on hand?)
If money is really a concern and you have no connection at all with St Joe, then go for St Paul Boys.
I guess you know some influential person in St Joe?
Which school you decided? I wonder? My son got both St Jo and co Ed offer but my son and I decided co Ed so if you decided co Ed also then we maybe classmate.