A study by the Arizona Legislature's independent financial analysts shows Gov. Jan Brewer's proposed overhaul of the state's sales tax collection system could cost the general fund nearly $140 million a year.

A second new study by the Grand Canyon Institute, which labels itself a centrist think tank, puts the loss at $125 million.

Both studies raise questions about whether the state can risk the overhaul as currently proposed.

The lawmaker carrying the bill in the House of Representatives said Thursday the questions raised by the Joint Legislative Budget Committee review may force revisions. Possibilities include a phase-in of the overhaul or "circuit-breaker" language that would kick in if revenues dropped precipitously.

The new reports come as lawmakers and Brewer's representatives continue to negotiate with cities and towns worried that the plan will hurt municipal revenues.