You can submit your own press releases but think if your time values more than how much you would pay a press release service. Just do the math and if your income/hour is higher than the cost of using a press release service submitting your press releases yourself mean loss of money.
Where you can find cheap press releases services ?
In my opinion best finds are in the webmasters forums. Many new services launch and usually they offer lower costs in the beginning , to get themselves a reputation.
Some webmasters forums are : DigitalPoint, V7N or Sitepoint.