That might help. Some people need still more -- 960 mg or more. Is the verapamil instant release or extended? Most people seem to get better results with instant than with extended. Yes, get on the D3 regimen ASAP -- it's a more effective preventive than verap with a lot fewer potential side effects.
There is practically no insurance that won't cover O2, but sometimes you do have to fight for it. I am quoting a passage here from a post by jon019:
"....OXYGEN!!!....life changer...saved my sanity, perhaps my life. over the yrs sometimes insurance covered it, sometimes not (always appeal any denial, for O2 have your doc write a letter of medical necessity). note that Medicare has just now approved its use for CH, and many insurers follow their lead. when not covered, i did self pay. either way, my out of pocket was about the same. cheap by any measure, especially compared to triptans like Imitrex, no side effects, fast when flow, mask and technique dialed in, more portable than the stereotype would indicate. don't let anybody dump a concentrator on you.......many a clusterhead bypasses all this nonsense and uses welding O2, "same stuff out of the same spigot"...cheaper yet, widely available....no insurance droids to get in the way. just don't tell 'em you gonna breathe it..."
As we have discussed and jon' mentions, welding O2 is a relatively low-cost option. Easy to get, set up, and use. I don't want to oppress you about things you don't have, but getting oxygen is worth almost any sacrifice you have to make.
I hope you looked at the link I gave you up above, particularly the part of that file headed "Treatments without oxygen..." None of those are as effective as O2 would be or the D3 regimen can be, but some might help you.