The new price for the Diana and the Holga seem very high to me, for what you get.
I suppose it depends what you are after... but you can buy what I would call basic 'point and shoot cameras' in either 35mm or medium format very cheaply on ebeegeebay or just cruise around your local junk shops. Personally I'm into 120 rollfilm and I've had a lot of fun with a couple of Agfa Isola cameras that cost me about the same as the roll films they took ;-)
Box cameras, too, can be fun at very low cost.
For the cost of a 'toy' Diana new, you could buy a 'serious' second hand camera that would be very useable - but presumably the 'not quite in focus or properly exposed' quikyness is what you are after?
I'm most familiar with 120 rollfilm. Have a look at the Agfa Click, Agfa Clack, Agfa Isola, Agfa Isoly, Dacora Digna / Ilford Sporti, Bella 66 and hundreds of other telescoping front 120 rollfilm cameras.
In 35mm the choice would be even bigger....