My electric blanket has a max watt at 150 how much money does that cost to run?

Put a timer on it so it stops and starts when you get up and just before you go to bed.

No.  Turn it off and turn it on an hour or two before sleeping.

It might save a small amount of money by heating a smaller space (the bed), especially only when you're IN it. Heating the bed all day negates your savings.

Also, put some of those savings into fire insurance, since a large percentage of residential fires are caused by electrics or by unattended heating devices.

Also, you cannot possibly run a thermostatically controlled heating device 100 percent of the time, so your maximum daily power consumption will be substantially less than 3,600 watt-hours, on the average, even if it's on "high" the whole time.

Why would you leave the blanket running all day with no one in the house or bed?  Turn it off when you get out of bed in the morning.  If you want the bed warm, turn it back on about 30 minutes before you bedtime.  

They can be a fire hazard and it is not safe to leave them running with no one in the house.  

WHY would anyone leave it on during the day. What happens it it catches on fire ? They can.

I can't say how much it costs you to operate it since I don't know your utility rates, but we can give some examples:

My own utility charges me about $0.125 per kilowatt-hour.  A kilowatt-hour is 1000 watts of electricity, for an entire hour.

At full power your electric blanket consumes only 150 watts, so that's less than 1/6 of a kilowatt-hour per hour of full power operation.  So your electric blanket costs, at the very most, about two cents per hour.

And this is assuming that when turned to its maximum output, its duty cycle is 100% - it is actively on and heating the entire time.  In reality it is most likely cycling on and off so its consumption is likely considerably less.

But don't leave it on all day.  There's no point.  If you're using it to warm the bed up before you get in, just go in and turn it on about an hour before bedtime.  That'll do well enough.  If you can't remember that, put it on a timer that does the remembering for you.

They say (they being the experts) that setting back your thermostat 7-10 degrees for 8 hours from your normal setting will save you about 10% per your heating season.

10% may not sound like much ....but if a bank is paying me 10% interest on savings ...I will take it any day. 

Using it for 6.67 hours on high will use 1kW/H of electricity. Look at your bill to see what you pay for this much. Guessing less than 20 cents.

Yes it will save you money, but not a lot.