I began researching kitty doors, the better rated ones were going for $40. That seemed ridiculous, and we might want two of them so that the litter box could be placed in the garage and it didnt seem that complicated to make one. So I did.
Spent $5 on the black vinyl floor runner. The rest was made from wood I had. Even has a little door to prevent her from going out or something else from coming in. Still needs a little finishing such as painting and filling in the gaps between the hole in the door and the kitty door. Olive loves it and goes in and out and then in and out again.