We had entirely separate invites for the evening reception. The reason was simple, all the people who worked for us wanted to come, as well as a large number of our customers. Basically if we invited everyone who wanted to come, we'd have been well over capacity for where we wanted to have our reception.
We sent ALL the invites to singles with a plus one. It was lovely, we made it clear that anyone who wanted to attend the church could do so, and many of our staff did. As they were all local we had a bus in the evening to and from the evening do.
We also purposefully chose a venue that had a hotel within and a cheap as chips Travel Lodge a 5 minute walk away.
We did this due to numbers, and we were incredibly touched by the amount of people who came to the ceremony itself, people were standing at the back 
To start splitting couples and dictating who can be part of the meal and who can't is mean spirited and mean, not frugal. Also if you invite people only to the evening do then you should lay on a separate buffet for the evening.
If you want a big wedding with lots of guests than save for it. I hate this me, me, me attitude that is prevalent in weddings now. Don't use it as an opportunity to reveal to others how little you think of them 