I just went through this on my Lexus SC430, after going through it on my LC. You may not like the answer.
1010keys, keylessbest, and a handful of other
ebay/
amazon sellers (who I'm convinced are all the same company) will sell you an unprogrammed, generic uncut blank for $20-30. I've tried a handful of them. Will they program? Generally yes, if the chip is correct. Are they as good as OEM? Not nearly. The range is awful, the plastic fit and finish is poor, and some of them use a cheap steel blade that can wear your keyway. I ended up keeping the $25 keylessbest key for the LC, but I had to do the remote antenna mod detailed in this forum just to get close to the range of the OE key. I would not trust it - it's just my backup. So that answers your question about cheapest.
The best comes from the dealer, and I'd consider buying during one of the SE dealer network sales and having it cut locally. My local Batteries+ store cuts my blanks for $25. All my programming has been DIY, even though the dealer and every locksmith will say that's not possible. The procedure is also in this forum.
The sweet spot I found is Dorman and Denso blanks. For my Lexus (which I believe is the same 'security' cut key used on later model LX470s), I found a Dorman blank for about $140, so $165 with cutting. Lexus dealer quote for OE was $219 cut, so a little cheaper. The 'name brand' blanks have printed FCC IDs, which I think is your quality tell. First, these were easier to verify the correct chip on. Second, I think they have more powerful transmitters, and the Dorman's range is identical to OE. For $54 savings, you give up the Toyota/Lexus logo on the case, but the plastic looks identical. It's possible these are actually white-boxed OE keys, but I'm not sure.
So, for $, you can have somewhat functional and reliable. For $$$$ you can have perfect, and for $$$ you can strike a compromise.