v2's run around $100 for a set for that board. fins are not cheap, but can drastically alter the boards riding characteristics. think like what a new prop does for a boat.

I'd pick up a set off the link above. worst case, sell them on here or another boat forum. someone will buy you out for what you have into them minus shipping. they do make a world of difference if they are the right fin. if your kid is progressing, will give them some comparisons to help their riding style if you decide to keep the board.