I wouldn't specifically call this a mastering compressor...but it's my goto on the mixdown bus, and I find I don't need to do a lot more in the4 way of any compression when I do my own "mastering" final touches.
Compression is one aspect of mastering and often one of the least important. Compressors used in mastering are generally quite expensive. it is normally the actual tone of the box that is sought after, the gain reduction too but not always. I often pass signal through any given compressor to apply the circuit tone with almost zero compression. These are often but not exclusively units that have discrete or valve electronics and transformer based I/O. There are loads of compressors on the market that meet this criteria you really need to go and listen if you want a tool that will satisfy this role in your own set up.
i mean if you're on a budget, I'd just get the best you can afford and then limit ITB
really we need a budget range to actually help you. but an api 2500 would be a really great start if you can even afford that