I was born there as well, and my parents were not communist activists.
What I remember are long lines for toilet paper, shampoo and shoes.
True, but this was mostly in the 80s (and mid-to-late 70s in some regions). Basically, the beginning of the end. Which brings us to...
People imprisoned and killed on the streets
At the time where there were long lines for toilet paper, that was quite unlikely. Killing on the streets was certainly not the thing, and even political dissidents were usually found insane, so that they could be put into asylums rather than imprisoned (that's when they invented "sluggish schizophrenia") - better from the PR perspective.
Certainly, for an average Soviet citizen to be killed or imprisoned by authorities in the 70s on, would be extremely unlikely.
My Mom earning $3 per month.
That part is either bullshit or meaningless (or both). For someone like a teacher, say, the monthly salary was typically between 100 and 200 rubles during that time. Factory workers actually earned more (cuz "proletariat"). I can't think of anyone in full-time job earning less than a 100, in any case. University students got 50 rubles per month.
Now, the official exchange rate was 1 USD = 0.8-0.5 RUB, but that was bullshit in any case, because you couldn't freely exchange them. So the only way to meaningfully compare is in terms of purchasing power. Now, for example, price in rubles for some common foods:
box of 50 matches - 0.01 rub aka 1 kopeika (they used it for change when they ran out of coins)
loaf of wheat bread (400 g) - 0.26 rub
loaf of dark rye bread (700 g) - 0.16 rub
1 liter bottle of milk - 0.46 rub
1 kg of sugar - 0.78 rub
1 kg of cheese - 2.20 rub
1 kg of butter - 3.40 rub
100 g of chocolate - 0.80 rub
ice cream in a waffle cone - 0.20 rub
Some other random stuff:
bus ticket (valid for that one bus for any distance) - 0.05 rub
tram ticket - 0.03 rub
evening movie ticket - 0.25 rub
soap - 0.14 rub
camera - 15 rub
ushanka - 14 rub
vinyl record - 1-3 rub
1 liter of gas - 0.10 rub
motorcycle - 1000-1500 rub
car - 3500-10000 rub
So it's still not a straightforward comparison. If you take food - say, milk; US average is $3.74/gallon, so almost $1/liter. If you go by the prices in rubles above, it would make the average Soviet salary of 150 rub equivalent to $300. OTOH, in US, most people spend most of their income on rent or mortgage, while Soviet citizens spent most of it on food, clothing etc. Average monthly gross rent in US is ~900$; adding that, you'd end up with $1200 per person, or $2400 per household (since both would typically work and bring roughly the same wage). This is pretty close to the average median income of an African-American household in US today. So, basically, pretty damn poor, but not third world shithole poor.
OTOH, car was a real luxury.