Does it matter how expensive the filter is?

So im looking into my sponge filters i got off ebay for around £3, because they are basic and cheap sponge filters, does this mean they are less effective?

Basically, should i splash out on a 'expensive' one or are my cheap ones fine?

Also, because sponge filters don't remove chemical waste, should i also run another type of filter? and if so, what type?

From my own experience, sponge filters are great for biological filtration. However, I've found that mechanical filtration becomes important in larger tanks (for instance, in my 24L guppy/shrimp tank, the sponge and java moss are fine to process all the waste products, but in the 6ft tank, I have the canister feeding into the walstad/undergravel system and an internal which assist in providing mechanical filtration as well as biological). I think a lot of what will work best will depend on your setup, how you maintain it (e.g. do you take the time to turkey baste after every meal? Or are you more inclined to be in a rush out the door? Are you after heaps of plants in your tank? Or are you using plastic fantastics?) and what you want to get out of it.
Perhaps see how the sponges go for a few weeks (cycle your tank, see what the maintenance routine you need to keep the tank going well is like), and then if you're not satisfied with the results, add in a box filter (similarly cheap but mighty little contraptions), another few weeks, if you're still not happy, try a canister/internal.
Keep us up to date!

I have a filter in now that sits inside the tank and you plug it into a plug socket to run, when you take the cover off it, all it has inside is a square sponge (I dont know what the type is called lol) I have one of them and I have two sponge filters available, I think im confusing myself over what filter is best, should I just run the plug in fillter and put the sponge filter with an air pump at the other end of the tank? Its only a 3ft x 1ft tank

Sounds similar to the setup I had at one stage with my 4ft- worked really well- just watch that you don't wash ALL the gunk out of your filters or you'll crash your cycle

To help prevent crashing, rinse 1 filter one time, and the other filter another time. That way both don't get "shocked" at the same time ^_^