Hi --
My well pressure is typically fine (lived here for 3+ years), but over last month have had about 4 or 5 times where ZERO pressure at pressure gauge. I turn off the power to well pump at the breaker and then after 5 or 6 hours (or overnight) when I turn it on again the water is working. But, seems that it's not just a one time occurrence but happening every few days or so now.

Some particulars.
Well is 80 feet deep. About 18 years old. Well pump is submersible. 2 wires, 1/2 horsepower. 220/240 power type thing. Seems no problems there either. Power at Square D switch is exact same as out at the well (its only about 25 feet away from house). 4 inch well pipe.
Have tank with bladder and bladder is intact/not ruptured type thing (tested through schraeder valve). Pressure is set to be 40 on and 60 off. Have checked with 3 different air gauges (in case gauge sucked) and the tank with no water in it is set for 38lbs. So, all seems to be perfect there.

Replaced Square D switch and nipple and pressure gauge with new one. It worked (had power turned off for about 6 hours for trip to hardware store and then install and stuff). Thought I was a hero -- but, guess not.

When the water does come back, it seems just fine. No extra sediment or anything. No issue with pump short cycling real quick. No issues with the pressure switch or anything not functioning as it should. Seems that just sometimes the pressure goes up to 60 (as it should to fill) and then just goes down as people use water and drops completely down to zero and stays there (I've never seen it - just that must be whats happening when it "goes away").
If I leave the pump power on at circuit breaker and don't turn off there...then, water doesn't come back on it's own -- even after like 18 hours. Only when I kill power for more than 4 or 5 hours. Have tried shorter time periods - but didn't work.

SO -- HELP! What might be causing water pressure to come and go like this?
Anything else to check except to have well pump pulled and check it (assume it's same age as well 18 years).
I have no idea what else to do except to call a well person and have them check -- but, they'll probably want to pull pump and probably want to replace.
What, if anything can we check before doing that as it's gonna cost big bucks. Also, what would be a ballpark estimate for a well pump (again 1/2 horsepower 2 wire type thing -- Installed). I know things vary from area to area...just trying to get ballpark that you think it might cost. I live in Maryland.

Thanks in advance.
PC