It kind of depends what kind of bike you want to get out of it. I’ve got beach cruisers and a hardtail mountain I converted to more of an urban bike with slicks and a singlespeed conversion, so I get the different kinds of bikes the Jube Customs bike tries to be.
If you want something that’s fun to throw around on the street like a big BMX I’d suggest buying a small framed 26inch hardtail mountain bike second hand. Give it a singlespeed conversion to simplify it and clean the lines, and get some nice fat slicks with a nice round profile (look for beach cruiser slicks not slicks for a mountain bike), and some nice fat riser bars. The pic below is one of my old bikes with some Electra Hotster whitewall slicks. It’s just a 26inch wheel and the rim is standard mountain bike width, but as you can see the tyre still has a really nice fat profile like you’re after.

If you’re set on the 24x3.0 conversion, probably the easiest way would be to look for a bike with disc brakes, and then have the wheels rebuilt with new spokes and the 24x3 rims. By the time you buy the new rims, spokes, tyres, tubes etc and then have a bike shop build the new wheels (assuming you cant do it yourself), I think its going to work out fairly expensive. Most of the 24x3 wheels you see are built for beach cruisers, so buying an existing wheel and fitting it to a mountain bike would likely be problematic, particularly in regards to sorting out the brakes.
If you’re after something more chopper/cruiser-ish I’d suggest keeping a look out for a brand name beach cruiser on
ebay/gumtree etc. You can pick up a 26inch brand name cruiser for generally $200-$400ish. Look for names like Dyno, Electra, Felt etc If you choose the right bike you can ride it as is, without throwing more money at it. My fiancé has a ladies Felt we got on
ebay for $400 in mint condition, it’s got drum brakes on the front, 3 speed hub on the rear, and the rims are 50mm wide so they have the same kind of profile as a 24x3 rim. I’m about 170cms and I’ve got a few Dynos and you can ride them all day and not feel cramped, because they’re designed for adults.