Give it a chance
You may just need to get used to the differences on the new bike. I don't think maintenance is any harder or more expensive then any other bike. I consider the three drain plugs a small issue. Use the short style box end wrenches and you can get to them easily. A lift will get the bike to a level easer to work on but, I do not have one. A jack will not help because a jack will always be in the way of one of the drain plugs. I have laid Three 2 X 10's on the floor to gain that extra inch and a half. A couple of flat pans will solve the problem of the three plugs and filter. The $150 sounds really high. Maybe as Bowhunter said although a complete first service will be more than that.
Valkyrie is definitely a nice bike. Never rode one but have ridden with one. Not a cruiser, definitely a different type of bike. May be to late if that is what you want. Guess you will either need to deal with it or loose a bunch of money. Six cylinder, heaver, more power, smoother, Nice bike. A little more money.
Parts and accessories are like any other bike. Expensive, If you shop around you may find some less than others. Maintenance is pretty much like most bikes. Oil changes and other changes not much different. Valve adjustment checks seem a little more often but they are way over stated. I had mine checked once in 42,000 miles after the first service. They did not need adjusted. Hourly rates are the same. You will find they have gone up a lot since you bought the Valkyrie. The wheel hub and brake do get in the way of checking air. I bought one of those cheap electronic gages. Seems to get in there OK. Sometimes I do hold the valve stem just a little forward to make it easer. You will not have any problem after you get used to it, I don't.
The seat on many cruisers seem to be not the greatest for long halls. I believe they are trying to get the bike lower. I went to a Mustang seat. Is about an inch higher. Not the first one to do that on just about any cruiser. The posture of the rider is different on a cruiser. You can change handlebars and seats to change position. If not you will just get used to it.
There is a bunch of happy Liner owners out there just like most other bikes. Give it a chance and you will be one too. It is not a poorly designed bike on the contrary I am very happy with my bike. Repair costs are not an issue because it has needed none. Rates and frequency are no different than any other bike.