I tend to go with the Count on this, but I'd love to be proved wrong.
If you want to give it a try, the cheapest way of measuring the sort of temperatures needed is with a type K thermocouple and a handheld readout.
The cheapest readout I know works well is the TM902C, for 5 or 6 bucks delivered from China and easily found on ebay. It reads in degC, so you'll need to convert if you think in degF, but the price is good.
The thermocouple itself is likely to be much more expensive than the readout. I buy mine locally (I'm in the UK), but something like a KHXL-14G-RSC-18 from Omega is good for forges. It's long enough and rigid enough to be able to poke it into the forge in the position you want, has a fast response due to the grounded junction and the sheath will withstand temperatures up into the welding range for Carbon steels. It will actually tolerate fairly short periods at up to 1368 degC/2495 degF, which is where type K maxes out.
http://www.omega.com/pptst/KHXL_NHXL.html
It works OK in a forge or muffle, because the idea behind the forge/muffle is to have a chamber at an even temperature throughout, so the thermocouple will be at the same temperature as the workpiece.
If you are using a torch, which gives localized heating, it is difficult to ensure the thermocouple has good enough contact to be accurately measuring the temperature of the steel.
However, if you heat the thermocouple and blade together and use your eye to ensure that the thermocouple is the same color as the blade, you'll get a pretty good measurement.
Color is hard to describe and is perceived differently by different people, but is actually a very good way of measuring temperature. Back in the day, there were instruments for measuring temperature that used an electrically-heated wire. The operator viewed the wire against the object being measured and adjusted the temperature of the wire. When it "disappeared" into the background, it was the same temperature as the background and the temperature of the wire could be read off the instrument.
Infra-Red thermometers can work well, but tend to be expensive once you want to measure high temperatures. They are also very sensitive to the emissivity of the object being measure. This is usually an unknown quantity until the true temperature of the object to be measured is known by some other method and the emissivity value in the IR instrument adjusted to get the IR temperature reading to show the true value.
