Neon sign transformers are the starting point for many beginners Tesla coils. They are a handy 12 kV peak unloaded and 30 mA into a short circuit which is current limited.
For more details and photos: This is my neat 2001 dual neon sign transformer (NST) supply. It used two old NST’s bought for A$40 from a local neon place and rated at 12 kV 30 mA each. It uses two power factor correction capacitors of 15 uF each. I used a remote power switch driving a relay but I did not have access to  a variac.

NST’s are a bit electrically fragile and need a filter to prevent overvoltage damage.  This one has inductors and a capacitor. Probably of doubtful efficiency compared to the later popular  “Terry filter”which uses resistors, capacitors and MOVs.

Eventually these were the basis of a 4 inch Tesla coil powered by two neon transformers.