There is one tiny airport near Groningen, viz. Groningen Airport Eelde (GRQ).
Usually, however, you'll end up flying to Schiphol International Airport Amsterdam (AMS) and taking a 2 - 2:30 hour train (every hour there's a direct connection, every half hour a connection with one easy layover). Plan train trip and/or buy online tickets in advance at https://www.ns.nl/en
The conference will be held in downtown Groningen. Here are a few hotel options, roughly in order of pricing, from low to high. You might also consider of course airbnb or other bed-and-breakfast options.
There are a few options for 50,- or less, with shared facilities or dorm rooms.
For 50-80, e.g.