I took a keen interest in these rifles about a month ago, but decided against getting one.
These rifles in .30-30 are not rare at all. Go to a few large gunshows and walk around. I found 3, in VG to VG+ condition, for $200 to $275 . No problem. Two of them had a 12 gauge barrel to go along with them.
It is the 219 in .22 Hornet that is rare and now becoming somewhat collectable. These are going from $275 to $350.
Before going forward, you may want to consider the main issue that exists with these rifles. If you open the action, and then accidentally squeeze the trigger, the firing pin will be sheered off (broken off) when you close the action. Extremely common.
Replacement firing pins can be found, but taking the action apart to install the pin can be like a Chinese puzzle. Many experience gun tinkerers told me it took them upwards of two hours, and they had to get a spring compressor to do it. Most gunsmiths refuse to do it for customers, because they would have to charge at least $100 for their time, which is half the cost of the rifle. At any rate, the first thing you have to do when you buy one of these rifles is to buy a spare firing pin (or two). You have to find them as used parts, at Numrich.
Also, the original 219 had a trigger system that is totally different from the later 219B, C, D, E, and L. On the original, the movement of the action lever (to unlock the action) actually cocked the hammer. On all of the later models, the opening of the action and rocking foreward of the barrel caused a flat rod attached to the barrel lug to plunge into the receiver and cock the hammer. Schemata of the two systems can easily be found online, so you may want to take a look at them.
Although the conversion of one of these rifles to .30-40 sounds like an interesting project, I think that it will end up being one of those debacles that results in spending an extra $100 on a rifle that costs $225, only to have an odd rifle that is only worth maybe $150. Also, the requirement of constantly watching out so as not to break the firing pin would take alot of fun out of the rifle, at least for me.
Although these rifles have beautiful wood on them, and nice original case color, they were sold as very cheap rifles for folks who could not afford a bolt action. They were the original Handi rifle. You may want to take that into account as well.
Hope this info helps.