There is a very good hostel in Shillong in the centre of the city - YHAI hostel. The bed cost was Rs. 120 per bed (including breakfast) when I visited 4 years ago, but I don't think it might have increased much. Facilities are basic, and I don't think they have wi-fi. But if you have a good dongal, you are good to go. There are also many hostels and homestays available. You can check on booking.com and hostelworld.com
Shillong is a lovely place to visit in summer. Here are a few place of stay you could check. Hotel lake view inn
Tea garden homestay
Nature lap stay
Nature homestay Hotel roi ki
Caddiopeia guest house Kindly check through MMT, Yatra, Tripadvisor, Airbnb and OYO