I'm completely lost when it comes to this

I don't realy do any fancy graphics and tend to just rely on irfanview.
I've been thinking of getting something better but haven't got a clue why
the prices are so different. I've seen paint shop starting from about £20
going up to photoshop at £450. and have no idea what I need.
The main thing I need is something for resizing, cropping, optimising,
adding text over, changing colours, creating banners etc.
What should I use for that?
I don't mind paying for something good, but don't want to go out and
pay £450 on something like photoshop if I never use half of it's features.
Advice appreciated.