Graphing oven temperature over time
Not sure about the acceptable fluctuations but probably the most common sort of sensor for those high termperatures is a thermocouple. There are three easy ways to get the data to a PC that come to mind:


Logging the data using a temperature datalogger with a thermocouple interface so it can later be downloaded to a PC. That might be good if getting your laptop / PC near the oven is a hassle.
A dedicated USB to thermocouple interface.
Using a multimeter with a USB interface and a thermocouple interface. That might have a bit of a learning curve to setup but might be useful if you see yourself ever using the other functions of a multimeter.


Thermocouples come in several types (type J, K, T etc) but the main thing to check is that the datalogger you select is compatible with the thermocouple, that they have similar connector types so it's easy to setup and the thermocouple covers an appropriate temperature range.

There are quite a few places to buy that sort of gear but it should give you a few search terms to use. For example on Amazon a pair of products I found searching on "USB thermocouple" and "thermocouple sensor" that might be suitable are:

USB Thermocouple Measurement Device for Windows® Linux®, and Mac®

3 Meters 9.8ft K Type Thermocouple Sensor Probe -30 to 400C

Another thing to be aware of is that some thermocouple sensors (mostly described as probes) are only designed to be inserted into hot substances, the cables attaching them aren't rated for the same high temperature but you can check with the supplier if unsure and it's not mentioned in the specifications. Also I'm not sure of the food safety of thermocouples so I wouldn't use them for measuring the internal temperature of meat without checking into that side of things, but it sounds like that won't be an issue for you.