Well if you have no budget, then probably shots of a "mouse" traveling through mouse holes and walls and such won't be very feasible. You could probably accomplish something convincing though using locales within a house that are more commonly accessible.

Personally, I would try just getting the camera to have as low of a vantage point as possible and experiment with tracking and panning techniques. Maybe take a low-friction piece of material and put the camera on that, and then push/pull said contraption around? I think the biggest thing here is not exactly how you do it, but making sure the audience doesn't want to go "oh he's just carrying the camera really close to the ground." I would do my best to solidify the illusion using accessible locations, as that would seem to be what is feasible at the moment and, even if you did have the materials or ability to have an elaborate set, it wouldn't be worth anything unless you establish a solid illusion of "mouse-view" in the first place.

Hope that helps a bit.

Attach it to an RC car and drive it around. It might have a cool effect, at least it'd be low enough to drive under furniture and stuff. As far as going through holes and stuff like that, the only thing I can think of is to shoot the POV going into a black hole in the wall and then cut scene out of black into the wall itself, so you'd have to shoot within the wall of the mouse creeping around. That might work some.

Corax also has some great advice there.

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Thanks for the tips mates. that was helpful