These cost me £15, which is excellent. Firstly, it works on my budget (yay!) and secondly, it meant they didn't have to be that great to be worth it. Even a small improvement in how close I could get would be pretty good value. They are basically magnifying glasses you can screw onto the end of your lens, and from what I understand you can get more expensive versions, but these are the cheapest.
They come in a variety of strengths, which can be combined or used separately. When they're all screwed together, it's a pretty decent amount of magnification. As per the Rules of Science, for each added lens the image quality goes down a little. However, it really is a very small amount. As someone who does not blow up their images large for printing and isn't super fussy, it's negligible.
For the following photos, I screwed all four of them onto the end of my 18-55mm kit lens. (For a little comparison, here are a few photos I took with my actual macro lens: some matches and a pretty carnivorous plant.) Seeing as how the dandelion clocks are out in force, I thought I'd start with them to test out my new lenses.
Bearing in mind these are taken without a tripod and just my not-especially-steady hands, I'm suitably impressed!
Wow. I can actually see how badly I need to dust it. (And how the painting I was super proud of is actually super scruffy, whoops.) For a point of comparison if you're not familiar with Warhammer sizing, I think that ghoul's head is about 4mm tall.
Conclusion: £15 well spent, and successful budgeting!