for small gold in a miniralized soil
the cheapist in minelab that could do the wrok is gp extreme
what is the cheapist that could do the work in other types white, fisher, ... ?
First for SMALL gold in hot soil, use a VLF for better results. A Fisher Goldbug II or Lobo Super Traq, will smoke a low power PI like the TDI or Infinium. Unless you are ready to buy a Minelab SD, GP, or GPX, just forget about PI detectors for prospecting, and get a good VLF like a Whites GMT.
ATTENTION! - This is my personal opinion. If you disagree that is OK with me.