K.E.
HA! 9 years ago I actually made a three dimensional Thomas cake for my son's birthday and i'm NOT a professional.If you bake at all, they are not that hard to do. you just bake a sheet cake to cut and stack as your engine cab and one in a small loaf pan to carve the round shape from. You can do this, really.
The icing is the tricky part. I ordered mine on line as deep colors can taste bad ( I did a red fire engine one year, and red can be especially un tasty unless you get the right kind.
So if you are absolutely NOT up to this, try the Cakery on Abrams or Casa Linda Bakery.
And take a lot of photos so your child knows what you went through when they grow up. My 12 year old is very impressed now!