Well Thomas - figured it might be time for me to pop in and say something. I've been around this rodeo for some time now. It used to be strictly prohibited to "ask what something was worth" on this Forum. That appears to have changed now so here's what I have to say about your Model 100 with cast-end deck and a Tiller. (And for what it's worth, most of the members on here already know my posts are fairly long winded
1st, prices are very very sensitive to location. In Indiana your Tiller appears to be worth BIG money, which surprises me. These Tillers had been fairly common across most of the Mid-west and I believed they were priced in the $100-$300 range depending mostly on condition. I don't really consider PA to be in the Mid-west but believed Tillers were fairly common there as well. The problem in PA is the rust. Yours look pretty typical to me for a PA tiller, and generally would be worth less compared to the mid-west. Along the east coast tillers aren't as common and tend to be worth more "at the right time of year" (basically spring). Complete Tillers with the right-angle gear box would sell for $200-400 and maybe even slightly more if they were in terrific condition. Since many are only really used for a short period during the year they are often in really nice condition even tho they are 40-50 years old.
You don't show a pic of the tines which are critical, and very expensive to replace, if you can even still find replacements. The rest of the tiller parts had been fairly bullet proof BUT in recent years I've heard of things actually wearing out. They are not really designed to be re-built. I had a machinist friend that did completely dis-assemble and rebuilt one, and he had to actually make several of the parts. The cover for your belt guard is missing in the pic so lots of things normally somewhat covered have been exposed and appear rusted, so I have to wonder about the condition of everything else.
You don't show a pic of the right-angle gear box which does fail on occasion, at least the bottom pulley, sometimes the internal bearings, and hopefully not either of the shafts. These boxes can be expensive to rebuild and use 3:2 ratio gears. While a fair number of snow thrower gear boxes are around and appear pretty much the same, they aren't direct replacements since they generally have 2:1 ratio gears.
So, all in all, based on what I can see of your tiller and can't see of your right angle gearbox, and assuming you can demonstrate that it works good and the tines are in fair shape I'd say it's worth about $100-200.
Now, it's not clear to me if you're going to sell the Model 100 tractor or not. It also looks pretty rough and rusted up to me. I see several holes on the frame have been added. The fenders are not correct and neither are the wheel weights. It's missing the front grill, doesn't have the correct seat, and tires look to be in rough worn condition. One nice thing is having the lights. All in all, even tho it's got all that typical PA rust, and assuming the engine runs good and the clutch shifts good, I'd say the tractor itself with the cast end mowing deck is probably worth around $150-250. If you were located in the Mid-west or more on the east coast it might be worth a little more, but my guess is your tractor does need some work to really get it back to good operating condition.
So - hope my info helps you out. You don't have a Gold mine. You've just got an old IH Cub Cadet that could be restored.