You could do the "Dave Wilson Nursery" high density planting strategy ... put 2 different apple trees, with the same kind of rootstock, 18" apart in the same hole. The proximity ensures pollination, helps to tame the vigor of the trees and keeps them smaller and manageable to allow for easy pruning and picking, provides 2 different varieties with different ripening times or at minimum 2 different flavors if they wind up overlapping in harvest ... just need to keep each tree on its own side of the hole with pruning a couple times per year, maybe only once. If you go this route, would encourage a little research to make sure they overlap during bloom to make sure they cross pollinate and also suggest disease resistant varieties, there are alot of those now that taste good.

If you just want to plant one tree because that's what you want to do, its a crap shoot at 200 ft. plus ... chances are you would be ok but you wont know for 3-4 years, so why risk it ? You have alot of options to increase your success ... grafting apples is very easy ... you could plant one tree and this coming dormant season, graft 2-3 scions from your other trees on to it or better yet from a friends apple tree that taste good, and now you have solved the pollination problem a different way. If you have never grafted, watch a couple you tube videos on it and you will say, "oh, that's it ?" There are many ways to skin a cat.

^^ Ooh, I didn't know multigraft apples were a thing!

http://www.davewilson.com/product-information/product/multiple-budded-apples

Here is a good link for you to view based on your interest in a multiple budded apple tree.

https://www.starkbros.com/products/fruit-trees/apple-trees/stark-double-delicious-apple

Since you are not looking for a massive quantity, i would also recommend a multi-grafted tree. I have a few multi grafted trees and i love them. they allow for a reasonable harvest over time. My 4 in 1 asian pear has me picking fresh pears about 1 variety a week for a month straight (might be one week in between the second and third varieties, all depends on the weather that season). So i am a big fan of them. you do need to take some care with pruning to make sure that you keep the varieties all about the same size, or one variety can take over.

You're fine with apples...I wouldn't be worried at all, even if the nearest tree is a half a mile away.... especially if you see honey bees or bumbles.

On the multigrafts- I like them a lot but...... Unless you keep a close eye on the trees with regards to pruning the varieties that have more vigor, it's easy to shade out a small slower growing graft and lose it. Also, you won't have much fruit till the entire tree gets to size. I have several pluot multigrafts and a fruit salad tree and at 4 years in the ground, they are just starting to produce enough fruit for a decent harvest, but not yet enough for canning or preserving, or even cooking. For my apples, I planted a row of 9 different apples 5 feet apart and will just keep them head height for pruning and picking ease.

IMO multigraft trees don't look as nice, so if you want it for its beauty I like the double tree idea that "Joe Blow" suggested. Around here it is nearly impossible to not get pollination, because there are so many wild trees around. I have a 180 acre farm and there is a very old Bosc pear tree right in the center of it. It over produces fruit every year, and I have to thin it like 50% if I want any fruit of substantial size. To this day I have no idea how it is being pollinated. ???? Closest pear tree must be a half a mile away.

I did some research online on this topic, though regarding a different type of fruit tree, and came to the conclusion that for home production you are likely ok at 300-500 feet or so apart, as long as there are no solid obstructions like dense hedges. The issue at hand is that there are various type of pollinating insects, some like honey bees will have a forage range of miles, though they tend to go back and forth to the same spot until nectar is depleted there before moving to another spot. Other pollinating insects may only range 20-30 feet on average. The point being if the trees are a few hundred feet apart, your pollination rate may drop by 5-10%, which is still likely plenty productive for a home orchard, but may be the difference between making a profit or not in commercial production.

Consider that exclusion ranges to prevent accidental cross pollination is often measured in miles, and even then there is a certain acceptable percentage of cross pollination allowed.

Interesting info - thanks for the all the comments!

I guess I could plant a tree and try, wouldn't hurt, and if I don't get good fruit set I could always plant another tree outside of the fenced-in area and hope the deer leave me a few apples in the fall. Could do the same with pears - one inside fence, one outside. I certainly have room on my property to do this, it's really just a matter of keeping the animals from getting the fruit. I really don't need *that* many apples and pears for just the two of us, so the losses from the other trees really wouldn't be any big deal.