i wil vote for any vintage horse shell if u can find one in good condition on the bay for less than a new strop (not easy), nothing like the horse shell, if not a modern made Solingen labeled calfhide
The cheapest strop you can get IMHO that will sort of work is the 2-1/2" wide one sold on fleabay by seller "theexbay". Not the 2" wide one, that is much too small. Even his 2-1/2" one is still pretty marginal. Think of it as a sacrificial strop on which to make your newbie mistakes on. It is cheap and expendable. Next up the list I would say Larry's "Rich Man" strop. Maybe the "Poor Man" is just a little too poor but it would sort of work, but go for the Rich Man. For eitehr one, see www.whippeddog.com. Tony Miller's strops are well regarded and he has from fairly cheap to not so cheap. His entry level strops are probably a very good value for the money. Fromm Ilinois etc strops, not so bad but I don't like the hardware. For unlimited budget, of course get a Kanayama horse shell strop while the maker is still alive. When he is gone, there will be no more. I have one and it is a joy to use.
The fact is, once you have the correct form factor and reasonable quality leather, they all accomplish the same thing. But super cheap Chinese strops or basically any excuse for a strop costing less than $10 probably will not meet those standards and will be essentially useless.