Just need to keep the water above the lead plates. You can see them inside with a flashlight.
Actually it's best to buy the heaviest battery you can find, but, what battery place has a scale? I just pick them up looking for a good heavy one with a good price as my batteries have always lasted at least 5 years.
Just make sure your battery charger isn't a battery destroyer boiling the liquid all the time. You can hear it if you listen carefully. It shouldn't be boiling after a full charge. That ruins a battery in a big hurry.
I would not pay that price you mentioned because it's too much money.
Go cheapest, heaviest but most importantly a good charger that knows when to float not boil.