According to myFICO (http://www.myfico.com/crediteducation/creditinquiries.aspx) the impact of a credit inquiry will vary from person to person based on their unique credit histories. However, in general, it is estimated that one credit inquiry will take less than 5 points off your score.
One tool you may be interested in checking out is called CreditKarma (https://www.creditkarma.com/). It is a free service you can use to monitor your credit and it allows you to "simulate" changes to your credit score by running hypothetical scenarios. In your case, you could setup an account with CreditKarma and then see the impact of one or more credit inquiries through the use of their Credit Simulator.
And as an FYI, CreditKarma's free service calculates your credit score based on TransUnion's credit scoring system. You may want to still check your credit reports from the other credit bureaus (Equifax & Experian) and check your true credit score using a service like myFICO.
Hope this is helpful to you.