El Mariachi was shot for just under $7000 and that was film costs plus a few hundred for miscellaneous expenses. The reasons he did it so cheap was:

1. He had a partner in his star Carlos Gallardo. They were childhood friends and both had a passion for making movies. Carlos had the town they shot in wired. He knew everybody and he was from a well off family. So he could get his folks employees free as extras or henchmen. He got the hotel, the bus, the turtle, the dog, his apartment, etc... At least $20-30k of production value free because he was able to talk people into giving it away for free. You need a partner or partners who can get stuff free.

2. Rodriquez wrote the script with everything free in mind. He knew he had those items and he'd been to the town before many times so he could write the script based on what he had avaliable. If you don't got it, don't put it in the script. They say write what you know. Write what you HAVE also.

3. The most important thing that never gets mention is Rodriquez already had 10 years filmmaking experience prior to shooting El Mariachi. He would make short films on Beta or VHS with his family. He had around 9 brothers and sisters so he got them to be in his short films. He recorded on video and edited on two VCRs hitting pause and play and rec. This taught him how to pre-visualize and edit in his head so he would know which shots to get and what he didn't need. A vital skill when you can only do one take.

Now Primer:

Primer is a better example to first time filmmakers as I believe the writer, director, star Shane Carruth had zero prior movie making experience. BUT, he was an engineer so he knew he needed lots of pre-planning.

1. He went to every location he had and shot 35mm film stills with various stocks until he got a look he liked then went to the local film distributor and asked how he could emulate that look on 16mm. They like what he did and his vision and helped him out and gave him a discount. EDIT: I also believe the preshoots were designed to find film stocks he could use with the natural light available since he had no crew or wouldn't be able to add lights to the locations.

2. Like El Mariachi everything was one take because more takes cost more money. He rehearsed and rehearsed and only shot what he needed. Something unnecessary in the digital age, at least until some of the GOP1 hacks started coming out. ^_^

3. Like Rodriquez he only put in the script stuff, locations and actors he could get for free. His house, his job, wife, friends, family, etc... He did get some actors through regular auditions, like his co-star, and the reason they wanted to be in it was the script was so good they didn't care it was free. Write a good script and people will do it for free.

Now Clerks

Shot for just under $30k, it's still a good example of what to do and what not to do. It shares a lot of the same things as listed above. He had the store. He had his friends and he got actors to work for free because they loved the script. So I'll list the main problem imho. Multiple takes. He wanted the acting a certain way and he wanted long takes so any error and they had to start again. This caused multiple takes of almost every scene. A no-no in the film age, but not as big a deal in Digital.

So in closing the main points are, you either need a great script that attracts people willing to work for nothing or you need a partner/s who can get stuff free. Yes...sadly I have neither at the moment....sob.