Towing Package?

You should just need the brake controller and correct adapter. Price depends on the controller you decide on. I have the Hopkins/Reliance. You'll have to order the adapter online, but generally you can get the controller at WalMart. Just make sure you get the one with the plug and not the splice in wiring.
http://www.hopkinstowingsolutions.c..._control.html?make=Toyota&model=58#guideTitle

 

<$100 should get you ready for brakes. Everything else will depend on what trailer you plan on towing (tongue weight, GVW, width).
You can get the cheapo strap on tow mirrors from Walmart. I used them for a couple days while moving from AZ to OR, but got tired of the vibration and did fine without them. But, I plan on buying a set of power adjust tow mirrors (flip up style) to replace my OE mirrors.

 

For the brake controller check the link I posted earlier, controller details are in there along with a really nice setup, specially since you said you won't be towing too often look at how he did his so it's completely out the way when not needed.

 

Craigslist happened and I totally forgot to upload these, anyways its the only plug thats not connected to something, look to the left of the parking brake.

 

Aside from the brake controller and possibly mirror extensions, you may need a weight distribution hitch depending on the trailer weight.

I have a Jayco X213 that weighs about 4,500 lbs dry and tows nicely with a weight distribution hitch. The trailer is 21ft with a rear slide that houses a king bed.