For the minimal capital investment, just refurbish/replace those fixtures that do not work properly at this time. Leave the ones that are working. Replacement ballasts are not low priced. Often I have seen new complete fixtures priced lower than the replacement ballast alone. In some instances, I have purchased new fixtures and used only the ballast from them. Changing the entire fixture would have been quite a lot of extra labor.
I note your comment about the electrician using salvaged and mismatched materials for installations on his own premises. I have done this in my shop and enjoyed the savings.

There's a lighting forum?

Yuppers

Lighting - NEW

Here is a link that might be useful: budget fluorescent rehab

I just bought 10 program-start, T8 GE ballasts on line for $90 including shipping. They can be used for one or two tubes, have detection for burned-out bulbs and are very efficient (power factor and lumens/watt). I will use them in the house and in the garage for frequently-switched lights, 4', 3' double and single and, if they fit, in a fixture with 4 2' tubes. I think that will use them up!
I still have to deal with the 8' fixtures. I have no choice but to go with instant start with those. I am planning to install switches on the individual fixtures so I don't have to fire them all at once and save the tubes from frequent switching. (I will also put another type of light on that circuit to get me into the area and, in effect, demote the 8' fixtures more to task lighting.) I have seen some good prices on good instant-starts too.