Extremely low cost high voltage power supplies
If you are looking for an extremely low cost high voltage power supply, a good place to look is consumer products that incorporate high voltage. For example there are electronic fly swatters that claim to produce 4kV! Of course the current is very low, and performance in terms of ripple, regulation and stability is not all that good. The electronic fly swatter may not even put out nearly the voltage claimed. However, if these performance related issues are not important in your application, or just need to generate a spark, you're in luck. Besides, you can find them for under $10, and sometimes even under $5. Other products to consider as a source of low cost high voltage are air purifiers, mosquito zappers, LCD display backlights, piezoelectric spark generators, and vehicle electronic ignitions.