I got 100 ovulation tests off Home Health - the cheapo dipstick ones. I only needed to use about 40 of them though! They really did work. And the bulk buying is better value of course. Hope you won't need to stock up, but getting loads at once is an excellent plan. Buying a box of tampons at the same time as a pregnancy test often works too!
Since your cycle is not yet predictable, if you have super cheapies start at cd8. Piss on one at some point in the afternoon/early evening. Once you think you are getting close to ovulation (ie the second line is getting darker but is not yet positive) piss on an extra one first thing in the morning until you get a positive. Have more sex. Job done.