For a sit down interview, a cheap wired mic, used with a decent portable recorder can get you results on a par with systems like the Sennheiser G series or a lower end Shure system.
For a cheap solution, look at the Audio Technica ATR-3350 lavalier mic and use it with a hand held recorder such as the Zoom H1, H4N or Tascam DR series.
The Audio Technica has a very long cable, so with careful camera positioning, you can position the recorder somewhere where you can monitor levels.
I would opt for a wired solution over wireless unless I had the budget for a very good wireless setup.
The other thing to bear in mind when choosing a wireless system is you need to make sure that the system you choose can be legally used. Some relatively recent models can no longer be used as a result of the digital tv switchover.
With the sell off of 4G licences, some systems will be affected by interference. The safe option is to choose a system that is 'channel 38' compatible. You will however require a license to use such a system. I believe it's about £75 for 1 year. See
https://www.jfmg.co.uk/pages/news/Ch38_proposed.htm for more info.