Well, what you're talking about isn't a shower, since guests would NEVER pay for their meal at a shower. Basically, you're asking for a polite way to do a rude thing and there just isn't one.
If I received an actual formal baby shower invitation, I would assume that the meal was being provided/hosted. Not sure of a good way to word it. But you know your family/group best, so it's up to you! Maybe you should do it more informal like your shower and just do phone calls?
TTC #1 since Sept 2011
Me: 33, DH: 35, DX: PCOS & MFI (low everything)
IUI #1-3 - Low Post-Wash Counts - All BFNs
IVF #1 w/ ICSI: Long Lupron Protocol - Freeze-All Cycle due to Severe OHSS ER 4/27, 33 Eggs Retrieved, 13 Frosties FET #1 6/5, Transferred One Perfect 4AA Blast, HPT BFP @ 6dp5dt Beta #1 - 209, Beta #2 - 508, Beta #3 - 1,059 EDD 2/20/14
If they are all family members and close friends they shouldn't care about paying for thier meal. I would send out the invites with the regular wording for a luncheon and then let them all know via phone or throw a piece of paper in there with the map to the restaraunt on it with wording of how much the meals are like "lunch menu is priced from from X to X" It's just lunch, it's not like it's a four course meal you are asking them to pay for. I wouldn't be offended.
Re: need invite wording help for non-hosted shower
Me: 33, DH: 35, DX: PCOS & MFI (low everything)
IUI #1-3 - Low Post-Wash Counts - All BFNs
IVF #1 w/ ICSI: Long Lupron Protocol - Freeze-All Cycle due to Severe OHSS
ER 4/27, 33 Eggs Retrieved, 13 Frosties
FET #1 6/5, Transferred One Perfect 4AA Blast, HPT BFP @ 6dp5dt
Beta #1 - 209, Beta #2 - 508, Beta #3 - 1,059
EDD 2/20/14