With valentines day coming up you can prob find some heart-shaped or love themed candy/stuff. Or better yet, if the shower is after v-day you might score some clearance items.
I don't know what is available there but I have bought flats of flowers like inpatients and put them in little pots. Print out some sort of tag that says something about thanks for being there to help their love grow.
Michael's here has lots of little note pads and various stationary in the dollar section, including journals. I put a journal, hershey kisses in a little bag.
Right now you can probably find some cute votive jars that you can put a piece of tule in and fill with candy and tie with a ribbon. You can also find cute little take out type boxes, champagne flutes, or a candy dish from the dollar store and do the same. You could also tie a bag to a cookie cutter (I saw a pack of three heart metal ones at the dollar store, which would work great.)
Make a little bag of snacks with gum, candy bar, nuts, etc.
If you are crafty you can get one of those little round tins and make magnets using the clear stones and put them in the tin. I think April and someone else did that for teacher gifts.
You could also do something similar that several people did for teacher gifts with a soda bottle. You could use it to fill it with chocolates/beverage stuff, stationary/candle, seeds/garden tools.
If you really want to keep down cost and make it easy on yourself, you could always do a candy bar... the great thing about that being is that all you do is set out the bags (which you could attach a cute label to, or just leave plain) and people bag them themselves. It's like having 30 girlfriends helping you make favors, lol.
If you wanted to go craftier, you could do frosted votive holders - you can buy the etching cream at any craft store, and votives are SO cheap. A first or last intial monogram could serve as the seating card, or if you do the bride and groom initials, they could just be on a table all together to grab at the end of the day.
(ftr, favors are so ridiculous to me. I hate them more than any part of party planning, lol.)