Cheap bike computer - for 12inch wheels

[Aussie cycler]

Can anyone tell me of a cheap ($20 - $40) computer that will work with 12 inch wheels.

My running program each week usually consists of taking my 6 month old son in our 'jogger' around the streets or in the park and I want to record distance, time and av. speed. I don't need any other functions really so it can be a very basic one.

Polar, Cateye and Sigma will not go down to 12 inches. What other brands can anyone suggest?

Thanks

 

[rek]

If you can't find one, maybe calibrate the computer to double the actual wheel rollout or something .. that way you can just halve whatever number it's telling you to get a proper answer.