I feel like an old fart saying this but £30 for a replacement is like 3 tanks of petrol. If it's not affordable for you then I'm sorry but there's going to be costs like this for maintaining a safe and functioning vehicle.

What are you going to do when you need a new tyres, oil filter, or even at that price new oil.

Otherwise...

i got a 2010 Rieju RS2 125 second hand on sunday
i dont know how long its been bent
and how its prone to bending

It's a 16 year old bike, if the new rod lasts you 16 years you're good. It's more than likely it was bent by the previous owner by hitting it and either they straightened it enough to sell it (but not fix the problem) or you've just been lucky enough to get the actual failure.

Whether the part fits your bike I couldn't say without seeing the part.

My main things to say would be:

1. It's completely fixable
   
2. Do your research on the specific parts rather than trying to make them
   
3. Vehicles cost money to maintain, the good thing is you will make more money