The cheapest way to get a result would be something like a Kworld USB tuner ...
KWorld 499u USB Dual Digital Stick is about £30 (I got mine on offer at Maplins for 20 quid). Maplin have there own brand tuners for about £20. There are other brands at similar prices.
If you have a computer that is less than about five years old, it should be powerful enough for TV recording and playback. Nobody around here is likely to recommend any software other NPVR.
AMD A75, 4 Gig, 1000 Gig, Nvidia N210
1 x Blackgold BGT3620 dual DVB-T2
1 x kworld USB dual DVB-T (IT9135)
2 x Hauppauge Nova-t PCI