cudamark is spot on when he says to get a 2-box for this (although I digress from his advice when he goes on to give various coin machines as other alternatives). Forget all the coin machines, large coils, and debates/choices of various standard detectors. Get yourself a 2-box machine.
Because here's the deal: Even though it's true that a standard machine can find jar and toaster sized items with ease (and even more-so with "bigger coils" blah blah), yet you're going to be continually bedevilled with the OTHER stuff that "standard coin machines" are so adept at finding: COIN SIZED TARGETS. Doh! And even if you dedicate your mind to "only digging the big" signals, or "only digging the deep and big signals", you'll perpetually be bedevilled going back and digging a bunch "just to be sure". I mean, you can't assume that soda can size objects (jars, toasters, etc...) will always give an "overload" signal for your standard machine. This is only true when the object is shallow enough to trigger that. So for example, a soda can or mason jar at 1 ft. deep might give a quarter signal, not an overload signal.
So with a standard coin machine, you will be perpetually digging all the small stuff, or spend all your time "second guessing" large vs small, etc....
But a 2-box machine (like the TM 808) will ONLY find large items. About the smallest item it can find, is a soda can sized item (or a door-knob sized item if you have it finely super tuned and close to the item). Thus for your purposes (where your primary objective is ONLY the large item, and you are NOT looking for individual coins), a 2-box unit is your key.
I recently hunted the yard of a deceased fellow, on behalf of the estate, for jars of coins. And initially, I showed up with my standard detector thinking "I'll just dig everything" or "I'll just ignore shallow small stuff". But 2 hrs and 100 pieces of junk later I was going to give up. It was a very junky farm yard that had had burn pits, pig and goat pens, parked tractor cr*p, etc..). So I went and got a TM 808 and that changed everything. Now all I could find was bigger items. And even THEN I got 100+ pieces of large junk (soda cans, tractor parts, tools, etc...) However, i came up with the sought after 4 or 5 jars of silver coins. Would not have been possible w/o the TM808. With a standard coin machine, I'd probably have still been out there today digging up endless small junk.