Not many years ago, the cost of hiring a consultant ranged from $20,000 to 40,000. Most small and medium sized businesses couldn't afford such fees.
Today, fees for credible consultants typically range from about $7,000 to $15,000 for most businesses to receive full service. Some companies, like TurboGSA, also offer different service levels that offer lower cost options, which may suit the needs of some firms.
While price is always an important factor, you should really focus on the value and credibility of the firm delivering the GSA consulting service. While you may not want to overpay for a large consulting firm with expensive big DC offices, you also don't want to hire a low cost provider with very little experience in dealing with GSA schedules, or a paper mill churning out proposals without regard to proper price and discounting disclosures and other critical factors. Afterall, this can be a major contract for your firm and you don't want to be subject to bad GSA audits because of a bad consultant.
Our GSA Self Assessment toolkit includes a checklist for evaluating GSA Consultants.