Your university will often have a grant or a fund for this sort of thing, which very much depends on whereabouts you are going and the cost-of-living in that area too. The going rate for most universities is around €250-€300, which goes towards accommodation and your living costs, although this can change depending on the university that you happen to be studying at. You can also get an additional €100 towards your stay if you have any special needs that need accommodating.
For more on Erasmus, check out our Erasmus article here: https://universitycompare.com/university-advice/erasmus-everything-need-know/
For more on Grants, Scholarships and Bursaries, be sure to check out our comprehensive guide, here:
For more on Student Finance, check out our informative guide here: