Since no one has said anything yet, I thought I would give you a few ideas.
I have done some of the components of a press or media kit at one time or another, but I have designed a whole kit to use for the website I have about the book I am querying. Unfortunately it is not online right now to show you with a website link, but I have included links to some others down below.
You can definitely do it yourself! It sounds scary, but it really is just information about you, a way to brag that is not boasting but helpful to anyone who wants to know more (and maybe spread the word in the news!).
You can just add a new page to your blog (at least with Wordpress), or a new page to your website, and title it Media or whatever you want, and you are off and running. If you do not have your own website, that is probably for another thread, but you can buy a domain name really cheap ($5 a year or less) and pay web hosting ($6 a month) and you have a website. If you use Wordpress for a blog, the rest is free. So, for the media kit, type in some information on your media page, and you have a media kit! Now, there are degrees of professionalism, so obviously it is important to notice what others are doing for your type of book or needs and see what you need. Are you going to be doing regular public speaking engagements? Include a schedule. Will you have a newsletter? Include a link to it so the media know about it. But, here are some general tips.
There are many examples on the web, but here is one from Oprah (she calls it a Press Room):
http://www2.oprah.com/about/press/about_press_pressroom.jhtml
and here is one for a non-fiction bestseller "You on a Diet"-
http://www.realage.com/corporate/press/pressreleases.aspx
Some sites call it a "kit" or just "media", but from my research they all have:
An author bio (sometimes this is buried and harder to find, other times front and center- you can use some of what you write in your proposal)
Press Releases: Include links to your press releases. You can create press releases on your own too, if it fits with author/agent/publisher protocol (I'm not sure how that works). I have done this for my sites and it works to get visitors and publicity. You can use PrWeb or other free sites, I think prnewswire is another one, and publish a free press release. Be sure it is well-written, because people will find your site through google searches for years to come from the release. Also, have something to say about it that is new. "I am an author" is not good enough for acceptance, but "This author has a groundbreaking new book on x" is considered news. Basically, find a spin to say something new or exciting and you got it. They have great instructions for press releases on their website:
http://www.prweb.com/pressreleasetips.php
Media attention information A list of notable news coverage on you or your material, or for Oprah, "global" information
Media contact: Name, email, etc. for who to contact for an interview !
Optional: Your schedule (are you going on a book tour and if so when and where?)
Your availability for functions and who to call
Any other facts about you (awards for you or your books, testimonials or feedback from readers or audience, etc.).
Your Face and Book Cover: Most author websites I see have author headshots available for download, and also an image of the book cover available for instant download. This is a little tricky to do, but possible to do by yourself if you do not want to pay someone to do it. Here is an example from a google search, though I have not had time to read her website, but it looks like a great example for authors:
http://www.debbieweil.com/speaking/media-kit/
For authors who will have a huge amount of media coverage, it may get too cumbersome to keep the page up to date (what a great problem to have!) so another person may be needed. Also, if you do not know how or cannot figure out in the time you are willing to devote how to download images, etc. then you might want to hire someone, but unless someone knows of a cheap service out there, I would just hire someone hourly to do exactly what you need (just a jpeg of your book cover, or your author headshot, available for download, for example, rather than the expensive set up of the whole page). If you have the money, you could hire someone to do the whole kit, but remember you need to be able to keep it up to date (news coverage, schedule, etc.) so conisder that cost- will you be able to maintain it once it is up, or will you have to pay for that too?
Hope this helps as a starting point.