Your original fishers are probably either mullard or telefunkens. Look to see if they are made in England or if they have <> on the bottom for telefunken (it will be on the base of the tube inside the pins.
$10 won't get you much for tubes. It's well worth $50 to $75 for an NOS pair of telefunkens or mullards. The mullards may have a sweeter sound but overall, telefunkens are great. Think of it this way, you will get 5000 to 10,000 hours out of 12ax7's/12au7's. So, for $75, that will cost you about 1cent per hour.
$10 won't get you much for tubes. It's well worth $50 to $75 for an NOS pair of telefunkens or mullards. The mullards may have a sweeter sound but overall, telefunkens are great. Think of it this way, you will get 5000 to 10,000 hours out of 12ax7's/12au7's. So, for $75, that will cost you about 1cent per hour.