What are the best options for multi channel help desks for a startup?

What I'd like to achieve is that all the support emails, live chat messages, Facebook comments and messages, and Twitter messages can be handled from one simple and clean interface. The key factor is the price, I can't afford to pay for overpriced products such as Zendesk. I'd be grateful for suggestions.

Here's some I've personally used and enjoyed:

• Intercom
• Uservoice
• Zendesk

Here's a list stolen from elsewhere:

• Canny (SaaS) - Free trial, plans start at $99/month
• Feature Upvote (SaaS) - Free trial, paid plan $29/month for all features, including custom domain name.
• Receptive (SaaS) - Free trial, plans start at $199/month, no limits
• Doorbell.io (SaaS) - Free for 2 users, paid plan start at $9/month
• UseResponse - all-in-one solution (feedback, help desk, live chat, knowledge base). Available in cloud and self-hosted.
• Wantoo (SaaS) - Free Forever, pro plans start at $50/month
• Userback - (SaaS) - Free forever, plans start at $19/month
• Amplify Connect (SaaS) - Free Forever for unlimited users
• BetaEasy.com (SaaS) - $89/month for 15 users
• Customer Feedback Portal by ProdPad (SaaS) - Free, paid plans start at $20/year
• Feedback Lite (SaaS) - Free Forever, paid plans $29 - $99 /month
• Helprace.com (SaaS) - Free forever, plans start at $9/month
• HunchBuzz (Saas) - $145/month for 5 users
• Keeping.com (Saas) - Free to try then $15 /month
• GetSatisfaction.com (SaaS) - $1200/month for unlimited users
• IdeaScale.com (SaaS) - $200/month with unlimited users
• IdeaTorrent.org (Self-hosted) - $500-$1500 one time setup
• Insitez (SaaS) - $49/month
• OpinionLab.com (SaaS) - approx $150 per month
• Qualaroo (SaaS) - $63 - $499/month
• Survicate (SaaS) - Free forever, plans start at $50/month
• UserEcho.com (SaaS) - $59 for 10 users
• UseResponse.com (Self-hosted+SaaS) - $500 one time
• UserRules.com (SaaS) - $99 for 10 users
• Usersnap.com (SaaS) - Free Trial. Plans start at $19/month
• VisitorEngage.com (SaaS) - Free Forever for unlimited users.
• Webengage.com (SaaS) - Free forever; paid plans start with $29/month
• phpback.org - Free and open source
• Question2Answer - Free and open source