Alan, I'm kind of shooting into the dark here as you don't mention what you expect to cut, how much at one time or how often
I don't know where you are but here in central New York craigslist has a boatload of good slicers to choose from Yes, you may need to sort a few frogs out to find a prince but you can find a good solid commercial slicer at a very reasonable price.
I don't know if there is a rule of thumb on blade size as opposed to the height of the product you'll be slicing but my experience is that slicers do their best work on product about 1/2- 2/3 of the blade diameter or smaller. For used machines you won't be paying much of a premium, if any, for a 12" unit.
One concern that is very real is to consider how much storage space you have, how much space you have to use it and how much weight you are willing/able to tote around if the slicer needs to be moved to use it. You also want to be sure parts are availlable so check around the internet before buying used. Medium and heavy duty commercial food service equipment can last decades so age is less important than condition and parts availability. If you aren't mechanically inclined then a nearby service dealer might be a big plus.
Power and design relate more to how easily the slicer can cope with slicing a lot of hard product like hard cheese or dried beef than in slicing other items. I can tell you from experience that cutting several sticks of air dried pepperoni at the same time can put a strain on even a $7,000 slicer. If none of those are going to be sliced in large quantity then power is likely not as important as the maker, condition and parts availabillty.
Slicers designed for home use aren't meant to be slicing for a long time or with any great frequency. Commercial slicers are generally rated as light, medium or heavy duty with the ability to slice hard cheese and the hours a day of use seeming to be the determining factors. We have Univex 8512 and a Hobart 2912 12" slicers. Both are considered medium/heavy duty machnes and are just a few years out of production. They sold for $5,200 and $6,800 at retail when discontinued. They are rated for 8 hours or more a day of use but not for large amounts of hard cheese-go figure. They are both 1/2 HP machines that weigh over 100 pounds. Believe me, we don't have a lot in either even after replacing all the worn parts and blades. The smoothness and quiet operation of either is a whole different experience than using an inexpensive home use machine like our original 10" job. The ability to cut from near paper thin to over an inch thick doesn't hurt either.
For comparison, our grinder is considered light duty commercial and is rated for 2 hours a day. Commercial equipment if tough stuff. A month's worth of 2 hours continuous operation a day is more than most of us will use in a ifetime. That same toughness means that used commercial equipment is pretty nearly bulletproof if bought in good servicable or repairable condition.
So, when all is said and done what you expect to cut, how much at once and how often ought to count for as much as price, condition and parts availability (and maybe service availability). A new machine of any price that doesn't have a parts and service network and a maker and distribution network that will ensure parts avaiablability for a few decades (at a minumum) will be no bargian
I suspect that you would do well to shop around for a good condition used machine in any of the commercial brand names for which you can get parts.
Good luck and let us know how things work out. BTW, please update your profile with a location so we know where you hail from.