Do you realise how difficult it is to get a sonic range-finder to detect 180 feet?
Go to the hardware store, buy a sonic range-finder, pull it apart, and use the components.
It took the designer just 3 months and $5,000 to design this item so I think you will be able to design something similar in 5 days but it will take just 3 days to pull the ready-made item apart.
I know you will be able to write the code for the microprocessor in 2 days and create the circuit board in 1 day, but why re-invent the wheel, just buy something already made and no-one will know the difference.