At 5k you have two options:
(1) You need to be a one man show and become profitable very, very quickly (5k is about three or four months of rent, food, etc.)
(2) Have everyone on the team work a day job and contribute on nights and weekends.
Number 2 is the better of the options because you can put that 5k towards business expenses and you know your team is dedicated to the project (note: this is how Firefox started). Unfortunately, you can't hire outside help, so the people you work with have to be very reliable.
Additionally, if you can become "Ramen profitable"* off of 5k, you become much, much more attractive to potential investors. Not only have you proven that your model can make money, you've also shown that you can use capital wisely.
Like many of the answers here, it really depends on your situation and the type of startup. If you possess many of the skills needed to run your startup, 5k might be enough. Chances are you'll need to spend more. Plan on taking any money you make and putting it right back into the company. Starting a business online is cheap with the right skills and resources. If you have never written a blog, do not have sales/marketing experience, have never owned or managed a business, and you're not 100% passionate about the company you plan to start, I'll honestly and respectfully advise you to sit on the sidelines and learn more before starting your first venture.
I started my debt settlement company with less than 5k. Broke even in 60 days, grew at 30-40% several months after wards, now am at a constant 15% growth rate. But I wouldn't advise it for just anyone with $5k, unless you have the skill set.
Think 5k and under without skills or minimal certification:
Growing Cannabis (where legally allowed of course)
It doesn't matter how much money you have to begin with... It matters how much work and effort you are willing to put in, and how well you will do in convincing others in following your vision. $5K is not a lot, but it is enough for some equipment, and if you can get people to work for equity, and an investor to put in the rest, then you have a startup.
It depends on the startup capital and operating expenses required by the nature of the startup you are looking to fund.
You might be able to use that to seed-fund a very low-cost operation in an area with low living costs that is focused on largely intangible deliverables; for example, some sort of web application software. Stuff like Amazon EC2, etc. has really pushed down the minimal investment needed to get some kind of boilerplate infrastructure going.
On the other hand, $5000 would be nearly useless to put toward a private space flight venture! :)
I've got a rule of thumb of mine regarding any investment, no matter the amount of money.
Invest either in:
a) your profession - if you want to generate money;
b) you health - if you want to preserve money.
What does it mean to invest in your profession?
What does it mean to invest in your health?