NIS will do it all but, as you have realised, will cost you around £1 a week.
Free Services such as, AVG, Zone Alarm, Malwarebytes, CCleaner and many others, will do the job just as well for a personal PC but you will, maybe, have to do a little more yourself in setting them up and some do not have an Automated Scan Mode set-up.
There are many of these services, just follow the threads here and you'll gather which ones people have. Each of us chose the one we use because we like it as opposed to the Opposition, few of us agree which is the best. In fact, if you read the Results of the Professional Testing done by the various Magazines, neither can the professionals.
I was about to say: "You pays yer money and takes yer choice" but there is no need to pay any money although I make a personal contribution, every couple of years, to those that I use regularly.