Thank you for the input folks :-)
Yeah I am considering stealing one from a cheap package, but I want something reliable and when scavenging from other devices it's hard to be sure of the spec of the individual component. I don't mind paying a couple of pennies more if I know what I'm getting.
Also, I've been looking at buying one of these thermometers for a while but the reviews of them are pretty bad, they all seem to suffer from quality issues unless you go in to the high end catering devices. So I'm thinking if I splash a bit of cash on the main sensor, similar to the catering models, but make the brains from arudino parts. I'll have a catering quality device with multi-function coolness, good parts doing the measuring and a at reasonable cost.
Typically the lead wire doesn't have to be rated for the same high temperature that the probe will be measuring.
Indeed mate, but in this case the probe is actually in a cooler environment than the wire is. Since this is feeding in to an oven and reading the temperature of a roast in there live. So the wire will be going in to the oven partially, subject to the highest heat. If it was being used as a candy thermometer it'd be different, but the feed through in to the oven is where the issue of wire coating becomes important.
I recollect from experience that Teflon is not rated at 300degC. You may need to insulate your wires with ceramic tubes (don't know their names) for the section that is very close to 300degC. I don't see other problems from your plan.
You're right, yeah Teflon is right on the edge of my requirements, I've seen some of the glass coated options, thinking I might be safer going for a higher rated coating. Thanks!