Actually, for purchasing, a limit order works. At least on all the online trading sites I have used.
STOP orders are for STOPPING losses. I guess my simple version wasn't enought... 😱
LIMIT ORDER EXAMPLES:
You want to buy some Microsoft. It is at $26.50 You make a limit order for buy 100 @ $26. If the price drops to $26, you get 100 shares for $2600.
You then decide that you will be happy to make $400 of this deal. You make a limit order for sell 100 @ $30. If and when the price hits $30, you get $3000 for your 100 shares.
You could also put in a stop order for sell 100 @ $25 just in case the stock keeps dropping and you want to limit your loss, or you could put in another limit order for buy 100 @ $25 to get more shares when the price is cheaper...