I'm Stuck - Help me put a motor in my Dalek

Last year I started to build my own Dr Who Dalek, It is a scale version of a Mk 1 Dalek which is the very first Dalek made in the mid 60's.
Building out of scrap wood I had, some pallets and some new MDF I tried to do on a tight budget. Unfortunately this has led to the Dalek being quite heavy and hard to manoeuvre. Also being 6 foot 4 has also made it very hard to fit inside. I have modified it making the inside larger for my arms and shoulders so I now just fit.

The TV show Daleks "Fred Flinstone" it to move, i.e. use your feet to push it along but me being tall means my long legs struggle to have enough room to do this.
I have seen where Electric Wheelchairs have been modified to provide full joystick control making the Dalek move quite well.
It was my plan all along to spend this extra $$$ (don't tell the wife) on a second hand chair but late last year I lost my job and now cannot justify the spend.
The Dalek will be used in community events and promotions and to bring smiles to kids and adults alike. Here is my daughter inside, she will need a cushion to see through the neck section. She thinks it is great fun.

Once finished, should look like the one below;