I headed over to Primark and bought a black roll neck jumper for £6. I sized down as I wanted it to be really fitted. Then I popped into the local market and picked up five gold buttons with an anchor detail on.
I worked out the placement of the buttons and sewed them on one by one with black cotton. It took about 20 minutes in total.
This is the finished jumper. The buttons don't sit quite as well and flush with the jumper because of the style of them. I think I'll keep an eye out for some other buttons to switch them with. Also the weight of the buttons is a slight issue as the ones on the neck cause it to droop slightly.
It is quite an easy DIY though and not a bad saving.
Balmain = £575
Primark jumper and buttons from market = £7.75