Do you have a logo and/or brand identity or is that something you might need help with as well? For pitch deck design, I've heard great things about http://investorpitches.com, but suspect they may not be able to stay within your budget. Whenever I need to find a great designer at a reasonable price, I hit http://dribbble.com and http://behance.net. You can also check out to http://elto.com and maybe even pickcrew.com - these last two resources might have a referral if they can't connect you with someone with expertise directly. I also have a designer on staff that could work with you, depending on the complexity of the design work you're after; we partner with a number of startups, mapping out the MVP and providing branding, marketing and strategic clarity.
If you'd like me to take a look at your deck for flow of content and/or strategic clarity, I'm happy to get on a call.