My 03 caddy yesterday will not move out of park on 2003 Cadillac CTS

Shift lever lights are not on , key is stuck, checked fuses they r fine what could be the problem, theft light is on and my gas gauge is reading empty

Asked by for the 2003 Cadillac CTS
have mechanic check
I have done that, they told me it was my ecu unit from the codes it gave to us. That is an $850 part at Cadillac, do you know of anywhere cheaper in the central Florida area