I looked at the LED fixture that are available in my area and I couldn't see spending that much to replace my shop lights. I have 30 4ft fixtures.
I mounted 5 plastic light sockets from lowe's (about $1.25 each) on a board the length of the florescent fixture. Screwed in 5 of the cheap 13 watt led bulbs lowe's sells( they were less than $2 each also).
I think the 5 were a bit over 4000 lumens. So far so good. They use about 15 watts less but are instant on and cold doesn't bother them.
I mounted them on a board so I could hang them from the chains that were holding the florescent fixtures.
You could mount them on the wall around the perimeter of the room if you don't have enough ceiling height.