I've had 24 of these in my home shop for a year with no failures. About $6.50 apiece and free shipping. Available in box quantities of 6, 8, or 10 tubes. All of my fixtures were purchased back in the 70's, and like yourself I had no desire to spend a bunch of money on new fixtures. 2/3 of mine were stacked in a corner to be thrown away due to dead ballasts, and would've been out with the trash were it not for the advent of bypass type tubes.
https://www.amazon.com/dp/B01CQ2ZKZO/?tag=atomicindus08-20
They will work as a direct replacement on T8 fixtures with electronic ballasts, or in T12 fixtures by removing the ballast. They're fed from both ends so wiring is as simple as removing the ballast, hooking the hot side to the wires from the tombstones on one end, and hooking the neutral to the wires from the tombstones from the opposite end.
I think the Sunco light output numbers are legitimate at 2000 lumens while some (not necessarily all) of the others with higher output ratings are overstated, as is typical of many Chinese products. A friend bought some others online with a 2300 lumen rating, at about twice the price of the Sunco's. We compared both side by side and couldn't detect any visible difference in output. In examining both closely, we decided it was likely both tubes had been manufactured by the same company as all the physical characteristics were identical.
Whatever you buy, make sure you get frosted tubes. The clear tubes with their "string of bright spots" are extremely irritating, particularly at low mounting heights.