I worked at a pharmacy for about 5 years ... We have had hundreds of forgeries (either in the form of altered RX, forged written rx, or people calling in claiming they are the doctors.)
Many people that just made alterations we would call the doc and verify the quantity, and them give them the medicine for the correct quantity (lots of times people would come from emergency rooms and change Vicodin to Vicodin ES, or HP, or they would change #8 to #18, or I have seen people change #20 to #120 ....
When people would have totally forged written scripts, we'd call the doc first and verify its fake and if they want to press charges. If the doc wants to press charges ... than the PD gets a call ... Lots of the forgers have police scanners, so we had to use some number for their main detectives office... When the persom comes to pick up the forged script, We would stall them until the police got there ... they would then be escorted in handcuffs.
Lots of times, when we were stalling them, they would figure it out ... and run like hell,
Sometimes ... the police would use their radios ... and the guy would hear it on his scanner ... and not get caught.
We even had a guy that would call the Answering service for the doc .. and he would pretend to be the doctor and check for messages ... We did not catch this guy (He did get caught at another store though)
You should not forge a prescription. You probably would not get caught, However if you do, it is totally not worth it.
You could try to convince your doctor to write for the proscar, however that is Fraud, so he probably would not do it.
I wish there was a good way to get the proscar or propecia both legally and cheap ... but i do not know of any way (unless your doctor gives free samples)