first off, secret clearances are expensive and take upto a year or more to complete; (my clearance took over a year for example) so finding a person that has one already is your best bet although, this may prove difficult as well. you may want to look at GOV postings of personnel looking for jobs or use a GOV recruiter for best results.
i just completed 4 site surveys for a new VoIP project for a GOV unit. total cost was about $2600 (not bad in my book; which included travel, hotel, car, etc. to the four locations in the US; may be higher for you as the hotels provide GOV rates that were about half or less of the actual cost (1-2 days per site))
some references for finding 'cleared' persons are as follows:
general dynamics - tons of GOV projects and people with clearances.
http://www.generaldynamics.com
government contracting services - smaller GOV services provider with a decent track record.
http://www.gov-gs.com
envision consultants - medium sized GOV contracting company.
http://envisionconsultants.com
also, a good site is government contractors; http://governmentcontractors.org
(check the 'resources' link on the left of the main page)
you will have to join the NAGC, national association of government contractors, to view the links for 'prime contractors' and others valuable information.
