DHT22/AM2302 or similar variant is cheap relatively easy to program but not super accurate. About £2.50 on Ebay, I've bought a few, one didn't work which made programming difficult! There are dual 5V or 3.3V versions
The bosh BME280 is about twice the price and very accurate but IMO a bit of a nightmare to program. It is also 3.3v. The main problem is that my compiler (Oshonsoft) has no support for BME280 so you have to handle all the commands. I think there are libraries for Arduino so this would make it much easier, most of the work has been done for you.
I bought one but after several reviews of how to program it, it's still in the bits box awaiting further attention!
Anyone want a BME280 cheap