I would do 5 singles. As you say, even v accurate timing hasn't been the magic ingredient, so I think you have to spread your effort over as many months as you can. Is there a way you can do some closer monitoring even without the U/S? I'm now aiming for single IUIs since 11 IVFs have failed to work and my 46th birthday is any moment. I was hoping to avoid daily bloods from CD11 (which is how my current clinic tracks LH surge) so bought a CBEFM.....which has proved surprisingly accurate despite this being a wacky cycle for me. I'm hoping to get better at interpreting it and use that to refine timing (really broke paying the last "hail Mary" IVF off my credit card) so I can avoid the tests that add up each month (like bloods, U/S etc). I'm also going to buy Jill Blakeaway's book because it goes into minute detail about detecting cervical changes that signal O.
If you could narrow the timing to the right day, then, since the swimmers last 24 hours, you could do single IUIs. I think for those of us hoping for that one miracle egg, the more months you give it the better, vs putting all your resources into 2 or 3 tries...
Good luck with whatever you decide