Hotel/b&b in Rome in May

Convents would be in that price range. You could contact them directly (Santa Susanna website has some listed) or use the Monastery Stays website. There is generally a curfew, so ensure the timing works for you. And there's typically little/no English spoken, and certainly no amenities like room service. Rooms are simple, typically without TV, phone, etc.

Check with www.cross-pollinate.com. We just rented an apartment near the Colosseum through them for May, and I was impressed with the service I got from Amy and Steve. They manage properties and they have their own hotel, The Beehive. I found them in the RS guidebook, so I felt safe using them.

you could try airbnb - you may end up staying with an actual person (as we did in Boston, but with our own room and totally left to our own devices) or may find a great apartment rental...I just plugged in 2 people looking for a place in May for 3 nights (just random) between $10-100 and came up with 235 results for a private home/apartment, and almost 600 for a private room...now, i'm not sure which area is the Coliseum area, but you can narrow it down...there is even one 'a stone's throw fr St Peters', private apartment for $89 a night...

I had good luck with the AirBNB website. Many low price accommodations. I used Villa Teresa for $60 per night. Three blocks from metro and private secure parking.