A lens in the 85mm to 135mm range would be much easier to achieve higher magnification with extension tubes. Tamron 90mm f2.5 SP macro lens (1:2) on EOS 7D
A basic rule of thumb is that to achieve 1:1 you need as much extension as the lens' focal length... so a 300mm lens would need 300mm of extension, while a 50mm lens would need 50mm and a 100mm would need 100mm worth of extension tubes.
In truth, you don't need quite this much extension, because it doesn't take into account the lens' native close focusing ability. For example, I can't recall ever using more than a 36mm tube on a 90mm 1:2 macro lens. With less close focusing lenses, such as 85/1.8, 50/1.4, 135/2, I've rarely used more than one tube, 36mm is the longest I have, but I've used 25mm and 20mm as well.
Reversed lenses are a pain in the arse, due to lack of control over the aperture.
Talk about cheap... this vintage Tamron manual focus 90mm lens cost me all of $20 at a local secondhand store... and that included a matched 2X teleconverter, lens hood and more:
This is an interchangeable mount lens, designed to be easily adapted to virtually any camrea system. It came with a Nikon Adaptall2 mount on it. Cost me about $40 more to get a "chipped" Adaptall2 interchangeable mount for EOS from China. So now I've got about $60 total tied up in it. I like this lens because it's relatively small and tucks neatly into the corner of a camera bag. Here it is alongside other macro/close-up lenses I use:Left/rear: Canon 100mm f2.8 USM Macro. Right/rear: Canon 180mm f3.5L Macro lens.
Left/front: Canon 45mm f2.8 TS-E lens. Right/front: Tamron SP 90mm f2.5 Macro lens.
It's a pretty capable lens, too.... not bad for about $60 invested!Bee on orange poppy
Tamron 90mm f2.5 SP lens at f11. EOS 7D camera at ISO 400, 1/400 shutter speed. Handheld, available light. Future poppies
Tamron 90mm f2.5 SP lens with 25mm Macro Extension tube at f11. EOS 7D at ISO 400, 1/400 shutter speed. Handheld, available light.
So, macro doesn't need to be expensive. Granted, I was really lucky to get this lens so cheaply. But I've bought other copies of it before, for under $100. And there are many other vintage, manual focus macro lenses (Nikon, Oly, Pentax and more) that can be adapted pretty easily for use on Canon cameras.
Adapted, vintage lenses aren't as easy to use as modern autofocus lenses with electronically controlled apetures, but many of those vintage lenses are still able to take great shots!