The concept of dollar-cost averaging in theory is a good one.  But only from the stand point of getting your money working for you earlier.  

Purposely spreading your purchases overtime to try and average out your cost not so much.  It either makes sense to buy the stock based on your objectives or it doesn't.  Justifying the purchase of a stock at a high price because you own some at a lower price or hope to buy some at a lower price in the future makes no sense.  

Further, while it is fine to buy some shares today with the objective or hope of getting more later when the funds are available - don't become a victim of tunnel vision.  There may be better investment options when you make the next deposit into the account.  

Unfortunately dollar-cost averaging is a long used tactic from the mutual fund industry - which more or less convinced less knowledgeable individuals to blindly add to their mutual fund position(s) every pay period.