From the New York Times:

Marco Rubio, the former Florida House speaker who has proven to be a stiff challenger to Gov. Charlie Crist for the G.O.P.’s Senate nomination, said in statements on Friday that he would reimburse his party for about $3,000 in travel expenses.
According to Beth Reinhard of The Miami Herald, Mr. Rubio said he had erred in billing the Republican party for eight trips. “Billing the party was a mistake which needs to be fixed,” Rubio said in the statement. “So, out of an abundance of caution, I am personally reimbursing the party for the cost of all eight flights.”
The move comes on the heels of disclosures by The Herald and The St. Petersburg Times that Mr. Rubio regularly billed personal expenses to a party credit card, a revelation that his opponents and national Democrats pounced on. The Democratic National Committee even produced a Web video titled “Priceless.”