I would less than $50 or so. 

Realisto is doing a coin burn as well from originally 3.6 million down to under 2 million.  Which means if they get up and running and start gaining traction....your $50 investment will be worth more than it would if you bought $50 when the coin cap was 3.6 million. 

Understand it is riskier especially in this environment and they dont have an MVP released publicly yet.  They do have a demo'd version screenshots on their medium blog release however.

I'd just buy a little on idex first. Think about a coin that has a working product and unlike bitcoin which has 21 million coins.  REA has a less than 2 million. 

It's risky and you could lose it all.   So if $50 hurts.  Try $10.  and skip a meal out.