Towing and my Prius

I have a 2006 Prius and just put a hitch on it and rented a 5x8 trailer from Home Depot to haul a Sauna that was broken apart, probably weighed between 200 and 300 lbs total. I am in Florida and flat territory and used I75 for about 55 of the 65 mile trip, I drove about 57 mph and had no problems. I did worry some about it because I not that Toyota says not to tow anything with the Prius. First off Home Depot wouldn't rent me their trailer because the clerk said I had to have a Reese hitch! I had a DrawTite hitch, the Draw Tite got lost in shipment so I ordered another from Amazon and it had a Reese label on it. So back to Home Depot but the little trailer I wanted to rent was out of service so couldn't rent it. In the meantime I went to Uhaul and no one around me had one of the 4X7's but they would rent me the 4X8 enclosed one however I didn't have the trailer light wiring hooked up so they wouldn't rent to me. Back to Home Depot and decided to rent the 5X8. I pulled fine and gave me no problems. Don't know how far you could go with the weight but it sure dropped my mileage from around 50mpg to 25mpg's even with the trailer empty on the way back home.