Your brush is your nail tool of your trade, and trust me as 'Trinity The Brush Slayer' I've ruined more than my fair share in my time!!
It should last way more than 8 sets and yes you're right in that potentially you will trash them more as a newbie but there are things you need to do to minimise that risk.
Usually leaving product in them is the most common mistake....this is because you are not cleanly placing the bead in the nail, it's a common issue for newbies so practice is the key. You need to ensure you are working with the correct consistency, a dry bead will be sticky and leave product on the bristles, a wet bead will leave slightly contaminated monomer in your bristles....both will harden and ruin the brush. So make sure the bead isvthe right consistency every time.
Rinse your brush in a little fresh monomer and the end if each client, paying a few pence for a small amount of monomer is cheaper than £20+ for a new brush.
And when it comes to brushes, good ain't cheap and cheap aint good, as they say
Cheap brushes will have poor quality bristles, badly wrapped ferrals and probably non acetone resistant handles.
CJP have some lovely brushes, I like CND brushes and I know there are lots of NSI brush lovers on here too as a start of recommendations