looking for a laptop with ubuntu pre-installed

You can save a bundle buying a modest laptop and installing a Linux distribution yourself. Don't panic! It's not that hard.

I'd suggest trying Linux Mint 19 "Tara" - Cinnamon (64-bit). It has a beautiful GUI running on top of Ubuntu 18.04 and is a snap to install. Honest, it's easy.

A quick search of Amazon laptops shows a bunch of suitable machines. The specs I looked for were: 14-15" displays + 8GB ram + disk size 121-320 GB + Intel i7  quad-core processor.  I found hundreds of machines ranging from $300 USD to... well, a lot more than you want to spend. But there are tons in the $400-$600 range that would be great.

The specs mentioned will perform spectacularly for you and easily accommodate a VM to host Windows.  

I found one at Amazon that looks very attractive. A Dell Latitude E5450 FHD (1920 x 1080) Laptop with Intel Quad Core i7-5600U 4 core, 8GB Ram, 256GB Solid State SSD, HDMI, Camera, WIFI and Windows 10 Pro for $549 USD. You could wipe the Windows install or, (IMO the better idea) make it into a dual-boot machine. Again, the Linux install makes that pretty painless.

(Oh geez, I may have just talked myself into it.)