To buy just one reel for practice, I'd say even decent-brand wire is not that expensive. Especially if you can get a small 0.7Kg reel. Best to practice with decent wire so if it doesn't go to plan at least you know it's your technique and are not wondering if its bad wire.
Buy a reel of lincoln wire from weldequip.
In the past when finding my way in this game I have been driven insane by cheapo wire that works one minute and not the next.
£7.00 for 0.7kg versus £15.00 for 5kg, the maths is easyish, cant be bothered to do it.
But it does rule out something that can make learning a more complicated process.
Always buy the best you can. With welding wire it is a false economy, think how much of this stuff do you use in a hour? not a fat lot.
There are a lot of good products out there, but there is some garbage, use something with a Name.
I bought four part used large reels off ebay , seller claimed it was approx 35kg in total , when I eventually weighed it all came to 22kG making it not quite the bargain described , I will stick to proper sellers in future selling Murex or similar wire , there have even been ebay sellers offering wire with ' slight surface corrosion ' , thats for the bin .
Think it's low quality stuff and definitely got lower recently. I normally buy small wire spools from there on an infrequent basis. The small wire spools used to be precision wound but the stuff they sell now is installed on the reel in a really messy fashion. More corner cutting I think. Doubtless the wire quality will have been reduced along with the shoddy winding.