You probably shouldn't be cooking plastic in the kitchen at all, hot plate or otherwise.

There are a couple people who use hot plates but I think the pots with stirring apparatuses will work better and afford better temperature control. Microwaves are super good for the hobbyist or small to medium sized business injectors. What works for one person may or may not work well for another. This is something you have to decide for yourself. As far as a hotplate goes, I avoid them simply because I don't make plastic in batches large enough to warrant using one. For me the microwave on the garage work bench works great.

Walmart, Kmart, Shopko, Home Depot, Target....all of these stores will carry microwaves in the 1000-1100 watt range for under a hundred bucks so they are affordable if you are cooking a cup or less of plastic at a time. You'll have a whole lot more heat control using a microwave for smaller quantities. The one thing small cups of plastic bring to the table that larger cups don't is fairly fast heat loss. You need to find a way to keep those small cups warm unless you intend to shoot all of it fairly fast. I have a sand-bed heater I made from an electric skillet pretty cheap for when I am working multiple colors, but smaller quantities.

Play around a little with different heating sources. If you decide on the hot plate you're going to need a couple very heavy bottomed cast iron pots to cook the plastic and you'll have to be stirring a lot to prevent burning.