I think you got it... send out a mass email invite telling them about your dinner plans with family... but they are welcome to come after! If that is ok with you.
Otherwise... its your day... don't stress it.
Im not sure on the cost... But I know half dozen people that have used them. If your planning a big wedding... they seem to be very helpful and take the stress off the day!
Good Luck!
Don't forget...
To Enter:
In a paragraph or two, tell us why you want us to photograph your wedding.
Entries will be judged based on your creativity and genuine need for help.
I would recommend going with the photog you love... if you did save some money and were not happy with the pics, you would be upset for a long LONG time! Its not like you can go back and redo them.