Ugh. PSP... 😉
The obvious inexpensive alternatives would be Pixelmator or Adobe Photoshop Elements.
The Gimp isn't really a native Mac app - and whilst it's powerful you may find it rather unfriendly in use. It does, however, have the advantage of being free. Personally I use the full version of Photoshop, but if I had to compromise, Pixelmator would be my choice.