I use a stainless immersion chiller that I hang in my HLT and recirculate wort through with a pump. It took a bit of experimenting, but it's really easy to control the temp. I have a ball valve on the pump output that I use to control the flow rate with, which is important. You need the ability to shut things off when it gets too hot and you also need to be able to control the flow out of the mash tun so you don't compact the grain bed. I already had the pump, so the only additional cost was the immersion chiller and the quick release connectors, which was all total, under $100. If you need to buy everything, it's a more difficult decision.