You can do a lot with just taking like couch pillows from your livingroom and quilts/blankets from your bedroom.
Experiment with that before you spend money on acoustic treatments
What it sounds like is you need to cut down on reflections. This means  treating the hard flat reflective surfaces with something that has absorption/deadening potential. You could definitely go low budget with household items. Blankets and pillows can work. Or you can go to a more permanent route with the Auralex type foam or QR diffusers to scatter the reflections. As stated already in the comments, you want to treat the back wall first, as that is going to be the source of most of your audible reflections. Second would be your side wall reflections. Cheers!
Oh and also: It's more important to do something with the wall behind you than the wall in front of you when recording vocals
My friend used some of those acoustic muffling tiles in a small area that he said worked well.
If your face isn't on video while your talking (like doing a voice over), you can just record the vocal whilst under a blanket. It's hot, but works pretty good.
Discuss and share music production techniques.