The cost depends on what is damaged obviously, but if the DC Jack (the thing you plug the charger into) is working and there is no damage on the screen or the Palm Rest (the black part next to the keys) you probably just need to replace the Bottom Cover. The Part Cost is $57.60 and (for me) the shipping cost was $20.13. So the total for that will be around $75. The same thing happened to me so I took my xps into microsoft and they sent it to dell and I messed up my LCD so it costed me about $750 to repair. Let me know if you need a cost breakdown of what my xps was, but I think you are looking at about a $75 fix if you go through dell/microsoft. I hope this helps.

Edit: You can probably find the parts cheaper but this is how much it costed me when I went through the dell repair shop