owlet monitor

I REALLY want to get one of these just because I feel like I'll sleep better knowing if his oxygen levels drop I'll be alarmed. I just don't want to take the risk of it, you know? My dilemma is that I'm a single mom and $250 + is not really in my budget to spend on this. I know, I know... it'd be worth it in the long run, but that's just how my situation is. Does anyone know of any device that does the same thing but that may not be as expensive? Obviously one that's just as effective. Any suggestions are appreciated :)