My first strategy involves the lack of paper invitations. We created a gorgeous wedding website with all of the information, as well as some interactive elements (a cheesy vow contest and a place for people to suggest music for the reception.)
This is not traditionally acceptable. Oh, well. All of our friends and most of our family are very comfortable online. I don't even know anyone's real address, let alone have time to address invitations. Since it's free and doesn't use unnecessary resources, I've got no regrets. I did phone both sets of grandparents to tell them we're engaged and to personally give them the wedding invite link. Other than that, we've sent the link via text, email, and Facebook.
According to stats I've seen, the average cost for 100 invitations is between $225 and $450, but some people spend as much as $2000! On invitations! People, do you realize how much good you could do in the world with $2000? I also read somewhere that invitations should be about 3% of the total budget, so for our budget, we should be spending $54-60 on them.
I'll take zero dollars instead, thank you. Web-based invitations also mean zero trees wasted, zero pieces of plastic stamp backing to throw away, and zero carbon emissions to deliver.
Lots of wedding sites offer free websites for couples -- if you are interested, take a look at mywedding.com, theknot.com, or weddingpearl.com. If you are goth or want something not quite so...um...traditional, check out nearlyweds.com -- but that one is $49, not free. Might be worth it, though, if the templates are your style.