How much does a new ebike cost? I've seen some online for like $150 but they must be junk. I'd be using it for fairly normal commuter trips on mostly flat ground. I've been trying to compare specs on the pricier ebikes, but its hard to understand what will make a difference. I'm gonna try to take a test ride at a shop, but I'd like to get a third party's opinion on what a reasonable price would be so I dont get dragged into spending too much or too little.
It depends on your expectations, partly. If you have owned and enjoyed riding a bicycle in the past, you might want to look for an ebike that will be of similar size and style. So for example, a lot of people seem to like their Lectric XP folding ebikes, and they're affordable (about $1000 IIRC) but decent, and there's a company selling high volume that stands behind their product, but if you don't relish the thought of 20" wheels (I wouldn't) then you probably want something a bit nicer. So you're probably in the $1200 to $2000 range.
I started out almost 3 years ago with a (~$1800) Ride1Up LMT'D. My criteria were:
step-through
torque sensor, not cadence sensor
upright, relaxed riding position
relatively light weight (some ebikes are 60-70 lbs or more, mine's about 50)
a front suspension fork
decent capacity battery
large gear range between lowest and highest (this can be figured in "gear inches" via online calculators)
and a throttle.
I lucked out with an internet-ordered ebike that I couldn't try out ahead of time, which turned out to be solidly constructed. It ticked all the boxes except the upright position, but I was able to remedy that with an aftermarket adjustable-angle riser (between the stem and handlebar). Within a year I'd changed the saddle twice, added a Kinekt suspension seatpost (a fabulous accessory that makes the bike ride like a Cadillac), and mounted a few other doodads like bright front & rear lights, bell, horn, pannier bags, and mirror. Probably I have $2400 or more in it by now. And I'm about to add a home-brew rear basket accessory. See what this hobby does to us?
But wait, there's more!

I like to go camping and sightseeing, and some places (Acadia NP for example) only allow Class 1 ebikes on certain roads and trails. Mine is a class 3 (throttle, and too powerful). So last month I picked up one of the Yamaha CrossConnect mid-drives, original retail price $3000, for a mere $1000 (plus a $150 assembly charge, plus sales tax). So now I'm in the process of tricking it out to my liking, too!

Yamaha got out of the ebike market here and their dealers are dumping the remaining inventory. My local Yamaha dealer won't do anything for me if this one needs repair, though, so I don't know if the warranty is actually any good, but their ebike motors have a good reputation for longevity and most of the rest is standard stuff that can be handled by a bike shop. I was taught by the salesman, though,
the proper way to disconnect the charger from the battery, and he cautioned me that I can render the battery unchargeable if I were to yank the cord off carelessly & break the connector on the battery case. All in all, not sure if a Yamaha is an ideal first ebike for a new person since the support structure has collapsed.
But there are some good ebikes at the brick & mortar stores, and usually they'll let you test ride them. Giant/Momentum, Trek/Electra, Specialized, Gazelle... I've probably missed some. And you'd have the same place for service when you need something adjusted or looked at. As you shop, make a list of features that you think are important to you. That will help you narrow down your candidates.
Or if you happen to be in California, go see Pedal Uma and have him whip up something custom just for you!