Recommendations for essential measurement/bench tools for HV experimentation
Oscilloscope is probably the one thing that will give you the biggest help. But 1MHz is a very poor bandwidth for an oscilloscope. A standalone oscilloscope shouldn't start increasing much in price until you reach 50-100MHz in bandwidth, and you'll need that much to do any sort of debugging in transistors.

You'd also need high-voltage probes. (100 or 1000:1 probes instead of the usual 10:1).

I wouldn't bother with the frequency counter; most oscilloscopes would cover that feature.

Just for some datapoints, a brand new Agilent DSOX2002A 70MHz oscilloscope has a list price of US$1230, and it looks like you can get used 50-100MHz analog oscilloscopes on Ebay for &lt; US$100 -- buyer beware. Stick with reputable oscilloscope brands like HP/Agilent, Tektronix, Lecroy, and avoid the other brands if possible. (Whereas for multimeters, you're generally OK -- I've used BK Precision and ExTech multimeters and they're fine.)