I am a dostoyevsky (19th century russian writer) fan and i would like to understand more precisely how rich or how poor his characters were. I understand 10 rubles were a lot of money but i want to feel "how much". Were 10 rubles in 1869 like 1000 dollars in 2018, or could it be even more? Perhaps even less?
A Russian source here estimates that in 1870 the average salary in Russia was 25.53 rubles. The same source estimates that an average laborer's salary in the 1880s (closest time period for which data is available) fluctuated between 12.925 and 15.575 rubles. So relatively speaking, 10 rubles was about 40% of an average monthly salary back then, or between 60-75% of a laborer's monthly salary. That should give you an idea of relatively how much 10 rubles was.
To convert those amounts to today's money, we have to do a lot of estimating.
The same source estimates that 25.53 rubles in 1870 was equal to $19.64 1870 US dollars through the official exchange rate of the time.
Putting $19.64 through this calculator here gives us the estimate that this amount equals to $353.48 of 2017 US dollars.
So to answer the question at the end of your post, 10 rubles in 1870 would be $138.46 in 2017 US dollars (assuming 25.53 rubles = $353.48).
Now, I would say that looking how much 10 rubles is relative to monthly wages is probably a better estimate of how poor or rich a character is, because even today an average salary in Russia fluctuates between $400-700 depending on the exchange rate between the ruble and the dollar. Since most commerce is done in rubles, that proves to be enough for people to live on, despite how little that may seem in US dollars.