How about a FPGA board? I'm not sure which one to suggest on that budget nowadays but definitely make sure it's supported by free tools. Beware that FPGA programming is so complex that it can be a career in itself.
I was going to suggest a logic analyzer but a cheap Beaglebone will handle most microcontroller I/Os easily. Just needs a level shifter to work on logic levels other than 3.3V.
A thermal camera also would be good if you don't already have one.
Great ideas RoGeorge though I don't now what a nanoVNA is really. Can you get a good 3D printer for £200?
Sorry both forgot to say I also have RPi stuff and a Fluke 87V. Also, Hakko FX-888D and PICkit3.
What about an EEPROM programmer? Are they, pretty much, all able to programme all, pretty much, chips?
NanoVNA is a budget vector network analyzer, mostly interesting for RF work.
You can take a look at the Ender 3, the first super cheap 3D printer with decent quality.
SPI and I2C EEPROMs are trivial to program using a microcontroller. Indeed, it's not hard to find really cheap EEPROM reader/writers that are little more than a USB microcontroller on a board.