I think the issue you will run up against is that the relatively lower cost cyclocomputers tend to offer either cadence OR heart-rate, but not both. They are basically two-sensor devices, and in addition to the basic speed sensing, you only get one additional sensor.
I looked pretty closely at offerings from Cateye, VDO, and Vetta, and I believe it was the case for all of those brands that you had to pick between cadence and HRM. (In my own situation I opted for a VDO unit with both wireless speed and wireless cadence, which I'm very happy with.)
Since you've already checked out Garmin, try looking at Polar, since they tend to sell higher-end computers. In fact, a quick scan at
www.peformancebike.com (who have a broad range of computer and wrist-version products) shows a Polar CS200 model that claims to have speed, cadence, and heart-rate, all wireless, for about $160.
Of course, at that price, another option might be to get a less expensive speed/cadence computer to mount on your handlebar, plus a separate (and cheaper) HRM to wear on your wrist (since no matter what you do, something has to be worn for the heart-rate sensing). Total cost might be well under the do-it-all product.