$5 Aluminum Chassis
I just got this lovely anodized chassis off AliExpress: https://www.aliexpress.com/item/4001280424688.html
The total was just $5.06 delivered from China! Shipping was 13 cents, next best thing to free ship. It's precut for those yellow plastic gearmotor modules that are everywhere. No immediate need or plans for it but I'll start scavenging goodies from my parts hoarde cache. FYI AliExpress sells a kit with motors, wheels and a ball caster but that one is ~ $17 shipped: https://www.aliexpress.com/item/4001280473233.html Helpful to refer to that listing just to see one way to assemble it. There are lots of holes & slots, and a 9g servo cutout on top. Mine took ~ 2 weeks to get here, that's very good these days.
The chassis is similar to this Makeblock kit: https://www.amazon.com/dp/B00SK5RUQY
I don't see any smoking deals on motors & wheels right now, these are all kinda pricey:
https://www.ebay.com/itm/233990257481 https://www.ebay.com/itm/233986129477 https://www.ebay.com/itm/152772494803
I've bought lots of those gearmotors in the past for $1 each, and complete robot kits with a cheap clear plex chassis, 2 wheels & motors and caster for $6. But not now! I've noticed big jumps in prices for Ebay China electronics, and free shipping is disappearing. Covid fallout? Dunno. But if you have some of these wheels & motors already like I do, this may be one of the last great deals you can snag out of China. Pick a color, any color!!