You can invest 50.00 it will buy you a fraction of one share. It will be vary safe in computershare. Their process is a little different than a broker,first send them the money,then in about 4 days they will send you a text saying your share is purchased,then set up your acc

I will research over on superstonk,to verify if one time is possible.

Edited to add: I would call computershares customer service number to verify if you can do a one time purchase