The original Rega Planet is well under $300 and still holds its own. Ooooodles of reviews can be found on the net, I'm sure.
The Rega Apollo can be had for a bit over your budget. I believe it is supposed to be better than the Planet.
I had it in my system for awhile. It is good and deserves its accolades as a great value performer. It can be had for 600 to 700 used.
If you can stretch your budget to 600 to 800, for one box players, there are others I would choose before the Apollo:
Resolution Audio CD55 (or CD50)
And even cheaper, at around 500 bucks, I would go for:
EE Minimax cdp
Consonance Opera Linear 120
I have owned all of the above players. As you can see I prefer tubed, or tube-like sound.
And they all have it. They are all musical and engaging players. Arcam is probably the most neutral....almost dry compared to the others.
I think the Linear 120 is excellent and may be the sleeper in the bunch. It has an engaging and soulful character. Just a touch flat dimensionally compared to better players. But this player (and most other Consonance products) is prone to operational glitches. Its price has been driven down because of this, but purely from a sonic perspective, I think it is tremendous for the $$.
My faves disregarding price are the Cary and Resolution Audio. The EE minimax is also very nice.