I find Cards and Pockets to be the cheapest. They have a print shop to where you can use their provided template, fill in the information and you can print it yourself on the pre-cut invites, or you can get them to print it. The price to get them to print it is actually really cheap. I got quoted for like a pretty complex invite and the whole thing was less than $200 for 130 invites. So if you're doing just one card and one envelope I definitely recommend going through them. However their designs are only for people who like plain invites or if you can design your own. Otherwise I'd say go with Invitations by Dawn or Wedding Paper Divas. They alway shave 20-25% off promo codes. If you don't feel like doing online necessarily, I actually went with Inspirasians and she's based out of Burnaby. I found her prices pretty reasonable and she offered 20% too. If you tell her Jenny Kim sent you she might give you a discount.
Oh! and I think it's fine that you have just RSVP on the invite. maybe in a smaller font just along the bottom?
Click on each tool to see a sample.