So, I did something dumb today. How much will this cost me ?

Don't feel bad Crambo we ALL make silly mistakes now and then. I know I sure have. If you poke around in your trailer you may find where they junction into the wiring. Then take a picture and use your old cord as a fish tape and pull the new one to the junction area and re connect. Using your picture as a guide.
As far screw ups go I would list this as a level 2 on a one to ten RV scale of screw ups.

As another poster mentioned make model and year may help someone give you more exacting advice.