Best cheap detector

Whats the best cheap detector under $300 for gold prospecting, new or used  probably none ? But What about a used Minelab X-Terra 705 Metal Detector or a new TX 850  https://www.amazon.com.au/Underground-Detector-Powerful-Detectors-Treasure/dp/B0CCV2KMFS?th=1

The TX 850 is the Chinese version of a Fisher Gold Bug Pro.
   I cannot tell you if this detector is any good at all but the fisher is very good and can function in the gold fields parks and garden and over salty beach sand in the vlf mode. The disc mode is not much help in the gold fields or on the wet salt beach sand. ( wherever ground iron minerals are high)This  detector is a piece of cake to operate.
     Personally from experience with Chinese metal detectors I would not touch the GX 850 with a forty foot barge pole.

The gold bug will not go more than a few inches into extreme iron mineralisation but it is great for small shallow gold in moderate iron minerals. A larger 11 inch eliptical coil is available and is great for beach work or where the nuggets are deep in moderately mineralised ground.    I like this little tecta because I can take it anywhere except don't submerge it, is not waterproof.. It is not a PI machine and is single frequency VLF at 19 Khz if I recall correctly.

thanks, what about a used minelab X-Terra 705

I had a 705 for a while but we did not get along well. I had problems with the mode changing features. Only used it at the beach without much success. I found it awkward to set up, however going by reviews, plenty of people liked this machine as a coin, jewellery  and relic hunter I traded mine in on a Gold Bug Pro with 11 inch DD coil.
   The 705 is a good machine once you have learnt how to communicate with it........That was where I failed with mine... I think we were not on the same frequency.

Features of the 705

Minelab’s proprietary VFLEX technology. This allows you to change the frequency simply by changing coils. You don't need another detector!
Standard 7.5 kHz Concentric coil is waterproof, suitable for detecting on beach and riverside.
Compatible with low, mid and high frequency coils - all 7 X-TERRA accessory coils can be used with the X-TERRA 705.
Automatic/Manual Ground Balancing, Tracking and now with Tracking Ground Balance Offset adjustment. This creates a performance advantage in certain areas such as wet/dry sand transition and hot rock locations, by setting the balance slightly positive or negative.
True automatic Ground Balance eliminates false ground noises so you can hear elusive small gold signals.
Four preset detecting patterns that can also be customised plus All-Metal mode.
Adjustable Iron Mask – designed for Prospecting Mode. This feature allows you to find desirable targets lying close to ferrous metals.
Effective noise cancel reduces interference.
Threshold tone for more accurate target ID interpretation.
Two Pinpoint Modes: Auto and Sizing.
Target ID stability – precise, solid responsiveness in high-trash areas enabling you to efficiently and effectively search sites with a high concentration of junk.
Also a great coin detector with highly accurate discrimination and numeric target identification.
Positive transflective LCD display providing a back light only in dim light conditions enabling better screen visibility in poor lighting whilst saving battery charge in well lit conditions.
Depth indicators, update continuously, even in Pinpoint mode.
Runs on just 4 x AA batteries.
Lightweight, balanced design (only 1.3kgs) so you can enjoy detecting for longer periods.