I have very poor water pressure at my house. One faucet on and the rest are pretty useless. I was told I have 40lbs at the sillcock. The manhole connection is 100 ft away with 50 lbs of pressure. The hookup from the manhole to my home is a 1" Pex line from a 3/4" city main line. This connection was made 3 years ago and being alone the pressure was never a problem. I am now looking how to increase the pressure so I can sell this house sometime soon. Is the 1" line causing problems? Can I install a pressure tank in my house? The city will install another separate tap-in water line for $3,000.00. Looking for an opinion... thanks.

Adding a pressure tank will do nothing at all to help you. Pressure tanks store water under pressure. They don't generate pressure. You might want to consider a booster pump such as the one linked below.

Flotec Multistage Booster Pump — 3/4 HP, 3/4in., Model# FP5722 | Booster + Sprinkler Pumps | Northern Tool + Equipment