I've already got enough projects to keep me busy for a long time and really wasn't looking for another, but sometimes motorcycles just happen.
There were two piston port DT1 engines on Craigslist. I went and looked at them, and the seller accepted my offer of $160 for the pair. Both are 1971 engines. The one with the carburetor looks like a fairly good one, and still has the standard bore, so is likely a relatively low mileage engine, and should be a good base for a rebuild. When I bought them I didn't have a project in mind, but figured I might be able to use them someday.
About a week after buying the engines a 1971 DT1 frame with the title came up on ebay. It was $129.48 with free shipping. I hadn't planned on another project, but it was cheap so I hit the 'buy it now' button.
At the Boone County Swap Meet I found a mid 70s DT250 fork for $45 and a set of '74 MX250 wheels for $40.
The DT250 forks use the same top clamp as the '73-'74 MX250/360 and SC500 forks, but with a heavy steel lower clamp. There was a MX aluminum lower on ebay for $22.50 with free shipping, so I went ahead and got it.
I went ahead and put it into a loose rolling mock-up to help see what else I'll need, and to figure out the direction of the project. I went through some of my other parts and found a seat and tank for it. I think I'd paid $25 for the tank.
The front fender is a used Preton Petty Baja. The exhaust is from a '73 RT3, but I don't want to use the '72-'73 style heat shield. I had a nice '71 and older style heat shield to use on it. The front and rear shield mounts are the same, but I'll have to weld nuts on for the middle two. It'll be a while until I get to this bike, but I think it's a great basis for a project for not a lot of money, and someday it'll be a beautiful motorcycle.