2002 Jeep Laredo I think I got scammed.

I bought my jeep about a week ago, and I am starting o notice various issues. I know this is going to cost me some $$$ to fix, or going to be a complete loss, but I just want to know what to expect before I even go and start paying diagnostic fees just to find out I don't have enough to pay to fix it.

Issue 1- Oil Pressure, the oil pressure seems to run higher than it should throughout they (Imean like a tick or two below the highest mark), and then every so often it goes all the way down, and my check gauges light comes on. I have to shut it off and restart in order to get it to go back to normal.

Issue 2 - Transmission Fluid leak- Took it to Wal-Mart for an oil change, they said it was leaking trans. Fluid, but couldn't tell me from where for some reason.

Issue 3- White smoke from exhaust. Not a whole lot of it but a pretty consistent stream as I am idled or parked.

Issue 4- Hissing sound on the rear drivers side, sounds like tire is losing air but only does it when the vehicle is on.

I was thinking possible blown head gasket, and the low coolant light did come on today. But I filled it up and it doesn't appear to have lost any. I know the diagnosis is going to be bad, but how much am I going to have to spend roughly to make it safe and reliable to drive?