The $300~ support level has been tested several times in the past few months (since ~september) and such support appears to be very strong. Breaching this level will probably result in further price declines of at least $40-$50 in the near term
I think 300 is pretty strong too, but different EW counts leads to suppose a breach to 275 is also probable.
Here is a chart of mine, using EW (I'm beginner in EW analysis so feel free to criticize and give feedback) :
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check https://www.tradingview.com/v/5KWjIxbQ/ for details and more explanations
Wave-C is always an impulse, meaning 5 waves and standard impulse rules apply.

As you have your chart labeled with the pink (III), the (IV) actually
can drop below the green iii according to the typical retracement of an impulsive wave. After a fifth wave is complete, the correction usually ends in the territory of the 4th wave of one smaller degree. In this case, somewhere between $259 (stamp wave-iii high) and $45 (stamp wave-iv low). It isn't an absolute rule, but it should be expected as an initial target. Since the April high is the 3 to Decembers 5, that is where to look for a bottom.

Thanks for the feedback RyNinDaCleM, appreciated.
So, if I understand your remarks
(please tell me if I summarized it wrong), you pointed 2 things :
- from EW rules my first C target ($300) is incorrect cause wave 5 of smaller degree, labelled (5), should at least go as far as (3)
- from EW rules my second C target (testing again $278 or ultimately $257) is correct - still - my "ultimately" is (from your experience) not correct since C can end up in between III (old ATH) and IV ($85 but lowest point inside this wave is $45). For different reasons I don't see 257 a possible breakable level but thanks for providing a classical initial target ; I didn't know about this.