Well that depends on if you want it drilled on the bottom for overflows or not

Tempered you cannot do this.. Well for a price you can but you could buy 2 brand new 150's with stands and canopies for the same price
Measure the thickness and decide how you want to run your filtration.. Once this is done you can call a local glass dealer for the piece which is going to run from 75 to 200 dollars just a rough estimate... And if you are going to replace with somehting you can drill for a sump system, might as well have them drill it for you too

probably an extra 30 - 40.00 which is what you would pay to buy the tools to do it yourself as well.. The latter being do it yourself NOT suggested if you have no experience there..
Also after replacing.. alot of hobbiests will get some plastic egg crate and layit across the bottom of the tank to better distribute the weight of rocks and orniments as this is probably a good guess as to a cause of the initial crack