Size of downrigger

I'm planning on buying a downrigger to add to my kayak. I'm debating between the Scotty lake troller, (about $75) and the Cannon Lake troller, (about $134). Most of my fishing will be on the Mult channel, W and the C, may do some fishing in the some of the bays on the coast, but don't plan on going after tuna, or fishing Buoy 10, at least not for a year or so until I get more comfortable. Any thoughts as far as which one will work the best for my intended uses, is it worth the extra $60?
Thanks
John

In my admittedly limited experience, it seems to me that that dropper weights and planing devices (dipsy divers, jet divers, etc...), and not downriggers, are the norm on the big C, willy and coastal bays, as you'll mostly be targeting fish in 35ft of water or less.

How does a lake troll hold up with over 4lbs balls? I use 8lbs and I still get blowback with salmon gear.  Likely move up to 10lbs.

lake troller is rated for 5# max. not sure what kind(s) of problems could arise if you went over that.

I have a cannon easy troll that I use for Kokanee fishing in open water.  For the willy and big C  I like most folks use weights, divers etc as DWB123 mentioned.  Don't let that stop you though as fighting a salmon without lead on your line makes it a lot more fun.  If you do end up using a downrigger in the rivers make to use braided line not stainless wire so you can cut it if it hangs up. 

I own a Scotty Laketroller, a Scotty Depthmaster, and a Cannon Lake-Troll, and have used all three downriggers extensively.  The Cannon Lake-Troll is my favorite downrigger, and I think that it's a much better downrigger than the Scotty Laketroller.  The Cannon Lake-Troll will handle up to an 8 pound weight, so you'll be able to troll much deeper with the Cannon Lake-Troll than with the Scotty Laketroller; it's much easier to raise and lower a weight with the Cannon Lake-Troll than with the Scotty Laketroller because the clutch braking system on the Cannon is much better than the primitive hand-nut system on the Scotty; and it's really easy to shorten the boom on the Cannon Lake-Troll. 

But the most important question is, do you have a pedal kayak or a paddle kayak?  If you have a pedal kayak, you can easily mount a large downrigger next to one of your thighs, so I would recommend that you buy the Cannon Lake-Troll.  If you have a paddle kayak, you have to mount your downrigger where it won't interfere with your paddle strokes, and it will be a lot harder to find a place to mount a Cannon Lake-Troll where it won't interfere with paddling.  You may have to mount a large downrigger behind one of your hips or between your calves, where it will be less convenient to operate than if it's next to one of your thighs.  But a Scotty Laketroller is small and low profile enough so that you should be able to find a place to mount it next to one of your thighs without interfering with your paddle stroke.

I bought a heavier downrigger than I was planning on, yesterday, and am thinking I should use a 10' leader of 30# mono or something I can break off. Guess I should add a pair of wire cutters leashed to it for emergencies but won't be fishing in rivers with it, only puget sound or lakes. 

I found a mint scotty 1080 strongarm for $120 and it seems awesome, solid yet compact and light.