Depends which copy you're talking about.
The old
Ibanez Edge trems are generally regarded as a good alternative, but cost wise I think actually work out more expensive to buy (
www.ibanezrules.com has them for $235, whereas an average OFR costs $160 odd as far as I remember). Last time I was looking, it was actually cheaper to import from the US rather than buy in the UK.
The
Gotoh floyd is quite highly rated, and costs a bit less than both the Edge and OFR.
There's also the
Schaller model, which as far as costs go, I think is fairly close to the OFR. Schaller make the actual OFR as it is as well.
Apart from these ^ most floyd copies aren't worth looking at IMO.