Well, I think your symptoms match Central or Complex Sleep Apnea, and in my view without ASV you would likely continue spending time and money with little benefit.
Used ASV machines are surprisingly affordable.
To keep up to date, you can occasionally check out prices at Supplier #2. (Link to Supplier List is at top of all forum pages.) Their inventory varies weekly or monthly, so one would need to keep checking periodically, and prices include professional cleaning and usually new water chamber and new hose and 6 month or longer warrantee.
I would recommend one of the following models:
1. PRS1 DS960 BiPAP autoSV Advanced (allows heated hose)
2. PRS1 DS950 BiPAP autoSV Advanced (doesn't allow heated hose)
3. ResMed S9 VPAP Adapt REF# 36037 (ASV and ASVauto modes)
4. ResMed S9 VPAP Adapt REF# 36007 (ASV but not ASVauto mode)
Or an alternative to ASV would be the ResMed S9 VPAP ST-A or PRS1 BiPAP AVAPS DS1160 or DS1150, but I think those are not any cheaper.
Another option (which would be cheaper and probably more comfortable than ASV) would be CPAP/APAP/BiPAP coupled with Supplemental O2. Supplemental O2 sometimes (meaning "in some patients") largely eliminates Central Apneas but regular monitoring (meaning weekly or whenever changing meds or when traveling, etc) of blood O2 levels (SpO2) while asleep is needed to avoid the serious dangers of getting too much O2, so you would also need to invest in a comfortable recording Pulse Oximeter (meaning one which is worn like a wrist watch, with separate finger sensor cup which applies less pressure on the finger).
Actually, I recommend getting a Pulse-Ox right away, such as are available from Supplier #19.