Cranksets have a number of parameters:
- Q factor: how widely spaced apart the pedals are. Note a narrow Q factor requires a frame that supports a narrow Q factor or else the crankset hits the chainstays. Usually if not fitting a racing style crankset on a non racing style frame this won't be an issue.
- Crank length: yours is probably 170mm as that's the only number that would be 170 in the specifications
- Chainrings. You didn't tell what kinds of chainrings the crankset has but usually there are 2 or 3, in some modern MTB cranksets only one. Triples may have different chainring sizes such as 26/36/48, 28/38/48, 22/32/44, ...
- Chainline, at what location the chain runs if on the middle ring (3-chainring crankset) or the theoretical average position on 2-chainring cranksets where the chain would be between those rings. Usually this isn't an issue if you buy the same style crankset, such as double (2x) or triple (3x).
- Bottom bracket attachment. Today Shimano uses Hollowtech II but some older/cheaper and no-brand cranksets likely still use square taper
- If square taper: how long spindle does the crankset require (that will affect chainline, Q factor and chainstay clearance so you can't be very far off from the ideal spindle length)
I would try to somehow find if your bottom bracket is square taper and if so, what length and try to guess if it's JIS or ISO. If it's Shimano then it's JIS. Then find a crankset that uses the same taper (JIS or ISO) and the same length bottom bracket spindle.
If you have a square taper bottom bracket and can't find a crankset that fits the same length spindle, and mismatch would be so large it isn't an option, then I would use this as an opportunity and upgrade to Hollowtech II although it means you'll exceed your budget. A Hollowtech II bottom bracket costs perhaps around 20 euros, not much compared to the cost of a crankset. Hollowtech spindles are far more durable than square taper, but if you have a frame with poor bottom bracket shell alignment then bearing lifetime could of course suffer.
However, with 50 euros you can't upgrade to Hollowtech II and if you swap the bottom bracket you'll likely exceed your budget anyway, so the best thing is that you can find a compatible crankset for the current length spindle (if square taper).
You can measure the spindle length by extracting the cranks and using a caliper. However ISO/JIS type needs to be guessed. If you have a bottom bracket tool you can extract the bottom bracket and see if it says Shimano which means it's JIS. If some other brand you might find what taper that brand uses by a Google search.
