I actually came to recommend a Surface Pro 1 or 2. It’s an old machine and may be very affordable used, but it is also fast enough to handle modern drawing software. Most importantly, it also has a true Wacom digitizer with 1024 pressure levels. Microsoft switched to the inferior Ntrig digitizer in the Surface Pro 3.
A SP1 or SP2 will give you a really good taste of the Cintiq experience for a bargain price. I am not an illustrator but even today after having this weird old brick of a computer for a few years, I really enjoy writing and drawing diagrams. The stylus feels great.
An iPad Pro may be great too, I don’t know anything about them, but an old Surface Pro will give you access to the whole world of Windows software, which may be useful to the OP.
It looks like Surface Pro 2s can be had for less than $300 on eBay.