So, as I mentioned earlier, if a sponsor offers 150k for a logo to be put on the shirts, or (generously) 120k if the shirts are sold in the summer without it, how many sales would need to be made to compensate for that 30k difference? (Remembering it's profit that needs to be calculated, not turnover).
Also, if your mates are buying it later then it is still a sale - the club will still get a cut, so factor that into the calculation.
And if they were my mates I'd be suggesting that if they can afford a holiday in Portugal, they can afford a nice shirt. The club shop sells some smart golf shirts if they want to keep it MFC related.