vaginapagina | spermicide?

I'm on HBC, but my fiance and I have decided we'd like to have a little extra reassurance at the end of every month that there are no babies growing in my belly, and I suggested spermicide.

someone here had recommended it to me, and the more I've thought about it, the better it sounds.

so now I'm looking for advice.

I tend to have a sensitive vagina so I don't want anything that might potentially burn.

I'm looking for something cheap, also. $10 or less would be great, $5 or less would be even better!

any brand suggestions and the like would be awesome! thanks girls!