87 crx smoke

Ok I recently picked up a 87' crx hf with 279kmiles and I changed the oil the day after I got it now before I changed the oil I didn't notice it smoke at all really but now there is alot of white smoke pouring out when i start and rev the car up once im driving i dont notice the smoke and when i restart after stopping for awhile there isnt really any smoke just if i let it sit for more than 45 mins so I'm worried its a head gasket or something but not sure. And if it was a head gasket how much would that cost to fix? How fast should I get it fixed worriing about damage to engine if I dont any help would be nice.

Very well could be the head gasket. They are known to crack apart between the 2 and 3 cylinder and then you loose compression between those two .When the car heats up and then you shut it off,there is pressure in the cooling system that pushes the coolant into the cylinder and then when you restar the coolant burns off.
You can check this by going for a drive and get it warmed up and shut it down and grab ahold of the top rad hose.If it is rock hard then there is likely air in the system, which means you are likely pushing it in from the cylinder.
Changing it isn't really that hard for your motor.Be sure to get the head plained and also be sure to torque the head properly.