That's where they get you, on the price of filters with a bagless vac. They say "Never buy another bag again - save loads of money on bags" etc, but then in the small print, they say that "we recommend for best performance, the filters are washable but should be replaced every so often." What happens is that they will usually use a paper post motor filter that gets clogged with carbon dust etc, and it wont be washable, and this will usually cost more than say, 2 packs of dust bags.
The pre-motor filters on a single cyclone cleaner will need washing every other usage for best results, and they will get dog eared and fall to bits before a year is up, and they will cost more than a couple of packs of bags.
You might think that you will save money with a cheap bagless vac, but in reality, if you want it to work properly, you will have the hassle of forever cleaning it out, and the expense of buying filters - which would in the longer term cost more than buying bags for a bagged vac.
OK you might say - bagged vacs need filters changed too - yes they do indeed, but on nowhere near the scale that a cheap bagged vac would need, unless you fill the bags to the point that they burst and then clog up the filters, or use cheap copy bags which burst before they are full.
Also, most people that buy cheap bagless vacs never bother cleaning the filters as often as they should do, so that when the vac loses suction, they either sling them out in the trash, or carry on with them till the motor burns out or they just don't clean the carpets properly any more. This usually happens with the space of 6 months to a year.
Then they go and buy another cheap bagless vac, and the process repeats itself.
Eventually they get sick of throwing out vacs every year, that they go back to bagged vacs, and rejoice at the fact that they work better for longer - despite having to spend a few bucks a year on bags!
If you want a bagless vac - you need a good one that uses multi-cyclonic separation, but even these still need filter cleaning - just not as much as single cyclone bagless vacs. The drawback is then that you end up spending a great deal more for them in the first place.
Either way - they will get your money out of you - but bagged will cost you a lot less in the long run.