Cheapo marcy set w/ curl bar and dumbbell handles is up on amazon: https://www.amazon.com/Marcy-Olympic-Dumbbell-Handles-Collars/dp/B000ASG0WO/ref=sr_1_4?dchild=1&keywords=dumbbell+handle&qid=1588866213&sr=8-4
The cap one is up right now too from a reseller: https://www.amazon.com/Barbell-Solid-20-Inch-Dumbbell-Handle/dp/B0010YOBB4/ref=sr_1_3?dchild=1&keywords=dumbbell+handle&qid=1588866213&sr=8-3 this one pops up all the time on amazon
Go with a kit like this
They use standard olympic weights, so you wont out grow them (unless you plan on curling 200+ lbs on each arm...)
These also mean you can add weight as you need to, and if you have the room, get a benchpress setup which uses the same weights, so you save space and money.