What caused my 2004 Buick LeSabre to abruptly die and when I start it, it just spits sputters , it runs a bit then dies. Repeat and does the same, when I step on the gas it spits sputters n dies.

crankshaft sensor or bad coil pack

A bad coil pack will just make it run very rough. A bad crank sensor or cam sensor on the other hand, will do as you described, as will a bad fuel pump. Luckily, all are reasonably easy fixes as even your fuel pump is accessible through your trunk. That said, The crank sensor involves pulling off the crank pulley, and the fuel pump in a GM veh is usually a little spendy, though a little cheaper on Amazon.

Most likely the Mass Air Flow Sensor. A plug in diagnostic tool can give the code. Approximately 240.00 + labor which is very easy and another 50.00 that they charge for the diagnostic test. Estimated 430.00 maybe a little less. You can a buy an aftermarket one a lot cheaper if you do it yourself around 145.00 total however you will not have a warranty more then likely as most mechanics prefer the more expensive part with approximately a 2 year or more warranty. Its the price of the part that runs the cost up. Just depends on how much you want to put into an older car or try to fix it yourself. 95% of the time it is either the mass air flow sensor or the crank sensor as buicks are notorious for this. Sometimes the mass air flow sensor may just be dirty as it is a good idea to use some crc [walmart] cleaner on them to clean which isnt hard either but you need to be very careful when removing the naturally aspirated air duct the mass air sensor is bolted to because the sensor inside is like the filament of a light bulb. CRC cleaner can clean it when accesses and misted with the CRC cleaner. If filament is already broken then it needs replace. This sensor sits inside the duct that runs to your air filter breather and is screwed on. An easy job to replace. Also make sure the wire harness at the bottom that connects to it is not damaged or broken which could also be the problem. Some oil change places can be quite rough when replacing the air filter and damage the sensor or the harness if they are not careful or reputable in there work.