Can you recommend a good one for my f&s eagle talon 12? My budget is about $200. Should I go with a portable?

Use the search function and search for fish finders. There is a few threads about this with some great answers and recommendations.

All of the depth finders on the market today are pretty good units. Any one you choose in your price range will be fine. For a kayak, I would not choose a portable. There is always a chance you could flip over and you would not want the unit going to the bottom. There is a company that sells kits that come with the battery, mounting plates and transducer mounts for kayaks called floattubefanatics.com. They aren't cheap, but a secure, reliable mount for the unit and transducer are important. Check it out.

I'm assuming your budget includes hardware for mounting (transducer arm, battery, etc.)?

 

If that's the case, and if you're not a DIYer, look at these transducer mounts so you can price out battery and fish finder appropriately.

 

http://kayakfishinggear.com/search.aspx?find=transducer+mount

 

FWIW, I built my own, but if I had it to do today, I would likely buy one of these. The one I built is similar to the $22.99 Trax system version, but I mounted mine to a cutting board/mount.

Fleet farm has elite4x for 169.99.  I have the elite4 with chart very good accurate readings.  Or lowrance just came out with the elite3x for $100.  Then that extra cash can put to battery/battery charger and your extra accessories you need.

Lowrance elite 4x HDI 

Lowrance elite 4x HDI 

This one