Before I finally made up my mind and bought a 90mm Tamron I relied on two setups, depending on what I needed.
For outdoors I used a 50mm F2 (standard lens from film era) which I mounted on between one and three 'extension tubes' which were actually cheap teleconverters I got on eBay and removed the glass from them. I could get more than 1:1 magnification (I thin some 2.5:1 but can't remember for sure). This allowed me to keep the lens a couple of inches or so from the subject.
For more extreme magnification I used a reversed 28mm F2.8 lens (from 1980s). I mounted this using a reversing ring mounted onto a cheap extension tube set I bought on eBay (about $20). This particular extension tube had the camera and lens mounts attached by a screw thread (as did the tubes between themselves) so I could screw in the reversing ring directly to the tube instead of the lens mounting piece.
This gave me some rather extreme magnification and surprisingly sharp images. The downside is that depth of field is very shallow and you have to get very close to the subject, about an inch or so I think. The other thing is that you no longer have auto iris control so you need to focus with the aperture full open and then turn to the desired aperture just before shooting.
I still actually use this setup occasionally rather than the macro lens as it can give me much higher magnification.
If you want to go to more extreme magnification like shots of tiny bugs and such you can go for a microscope with a camera adapter. I bought a 'student' microscope for about $150 new on eBay (you can get better used ones for less) and an adapter tube for another $15.
This is a photo of a hard disk head taken with K-30 through the microscope.It is just about a millimeter across. It is actually a composite of about 50 images which were then focus stacked.
To give an idea of the scale
this is a photo of the same head shot with the Tamron Macro at 1:1 with a 10 cent coin for scale. The photo is actually cropped to half its original size (effectively magnifying it 2 times).
This is a mosquito also through the microscope and focus stacked.
And a fly
If you want to shoot bugs in this way then they have to be either dead or drugged, unless you can otherwise convince them to sit still while you shoot the 50 or so photos.
This is the CCD from a Canon compact P&S camera, actually just a corner of it. The whole sensor is about 5mm across but the photo is showing only a tiny fraction of that. You can easily discern the actual RGGB photosites in the upper left part of the photo.