Hi Ragnhild,
It's great that you are visiting the Aran Islands next month !
First of all, which one of the Aran Islands will you be visiting ?
Assuming you arrive on Inishmore (the biggest island of the three) , there are plenty of accommodation options near the ferry port. You might want to look into hostels (such as
Kilronan Hostel) since you are looking for an affordable place to stay. Furthermore, here are more
accommodation options in County Galway
Renting a bike could also be an option, it's a fun way to explore Inishmore during your time here and you could reach other accommodations further, given that you are travelling light.
Let us know what you think. :)
Antoine