Rink costs

Rundown of my rink costs:
1) 2x6 wood.  Free (craigslist; a neighbour took apart their deck).
2) White poly tarp (approx $75).
3) Wood screws (approx. $12 various sizes, lots left over)
4) Floodlight fixtures x3 ($15) and lightbulbs
5) Metal stakes/poles ($10)

6) U hooks for the poles $5

7) Water? 19x38x6" ?