I don't know if it will totally solve your problem, but note that you misspelled $item['varprice_arb'] on that third line of code. Assuming that error is also in your actual code, try correcting it and let us know if that's enough to fix the problem.

(Also, there's no semicolon on the end of the first line, but I'm assuming that that's fixed in your actual code, or else it wouldn't be able to run at all.)