The textbook answer is to value a floater as if it matures at the next coupon payment. See this link. http://breakingdownfinance.com/finance-topics/bond-valuation/floating-rate-bond-valuation/
Using the risk free+spread on the loan as the discount rate will result in a value of 100. Prices above or below par will be due to a change in credit quality. If the credit quality of the borrower has deteriorated since the loan was taken out, and therefore the spread on a replacement loan would be higher, the loan will be priced at some discount to par. Alternatively, if the credit quality has improved since issuance, the loan should be valued at a premium.