Invest in a new DSLR or Buy a used older model?

I want to start taking pictures for people but I don't own a good DSLR

I'm looking at the Canon Rebel t3i which is 499.79 with tax and all on Amazon (which I found in like new condition)

Or I've looked at a Nikon D80 which is much older but could still get the job done for about 350

Currently I have enough money to buy the D80 and i'm so anxious to start taking pictures. I'm not sure if I should buy the Nikon D80 or just save a little more to get the canon rebel.

Also: I'm am a Videographer and want to do small projects with the canon rebel t3i, which I would not be able to do with the Nikon d80. But once I get a camera I can start advertising myself to others and make money from taking pictures and save to buy canon rebel t3i

"I want to start taking pictures for people but I don't own a good DSLR"

So? I spent several years without a DSLR and I took some nice pictures.

"But once I get a camera I can start advertising myself to others and make money from taking pictures and save to buy canon rebel t3i."

Let's put this into different scenarios and see how it holds up.

"But once I get a car I can start advertising myself to others and make money from taxi-ing and being a chauffeur and save to buy a Bentley"

"But once I get a pair of boxing gloves I can start advertising myself to others and make money from bodyguarding and training young boxers and save to buy better gloves"

"But once I get a guitar I can start advertising myself to others and make money from gigs and shows and save to buy a 1959 Les Paul"

"But once I get a pencil and paper I can start advertising myself to others and make money from copywriting and save to buy a word processor".

Each of these is missing one step: application and talent. I'm assuming by the total lack of patience exhibited in your question, and an almost certainly total lack of understanding of what it takes to be good at something, that you are indeed in the teen bracket and (probably) a girl (yeah, sue me. Nearly all of these ridiculous questions come from teenage girls, and I can prove it with statistics).

The actuarial tables suggest that you should live for at least 70 years. Believe it or not, you don't have to achieve everything before you're twenty.

Fhotoace is a gentleman: he is telling you exactly what I'm, but more diplomatically. You almost certainly have a vastly over-inflated sense of your own talent, no concept of what is needed to excel in a field, and an assumption that having a camera automatically entitles you to be paid.

The Nikon D80 is a fine camera and can produce excellent images IF you have have the skills and expereince necessary to produce marketable photos.

You call yourself a videographer. Where did you go to school? Did you get a degree in film making?

You seem to be ready to jump into the commercial world of photography and videography, yet do not even know what kind of equipment to buy.

While in school, you would have had the opportunity to use different cameras and other gear associated with shooting photos and producing videos.

My guess is that you think you can call yourself a photographer if you own a fully adjustable camera and a videographer if you own or want to own a video camera.

Breathe.

Take some time to learn the fundamentals of photography. Plan on spending at least a year or two learning how to use your camera, whether it is the find Nikon D80 or Canon T3i.

You are being premature advertising yourself as a photographer or videographer without understanding the basics as well as having used the equipment for a period of years.

Here is the deal. If you spent $35,000 for a complete set of master mechanics tools, would you start advertising yourself as a NASCAR mechanic? If you bought a nice single engine aircraft, would you then start advertising that you are open to providing aerial tours?

Where in you idea of being a photographer or videographer, do you slide in the part where you actually learn how to use your equipment?

You may want to talk to a few working pros in your area and see what it really takes to work as a photographer or videographer.

I bought my first DSLR when it was a black friday sale (MY FAVORITE for big purchases)

Another thing you have to consider is the cost and quality of the lenses you will be needing/using.

It sounds like you're in a hurry, which is understandable, because photography is fun! But weigh your options carefully, because once you get in, you'll be tempted to upgrade often. Trust me, I know.

(So that's not a direct answer, but some suggestions)

Buying a DSLR is not an investment.

Buying lenses is an investment. Your camera body will be out of date long before your lenses.