RD-93s cost is for now around 2.5-3.0Mln $$, depending the order, larger the order, lesser would be the price.
The export price would be somewhere around 20Mln $$ or even more, depending on the avionics suite and clients requirements. I see a figure of 20+ upto 25Mln or so, the 15-17Mln price tag for now is for Pakistan and China, as these include no profits being charged, and the money invested in the project is also to be recovered and added in export prices.
Bringing in western engine would add further problems, as it would need further testing, it will be expensive driving up the price of JF-17 and the engine can not be re-exported to everyone, thus it will bring additional problems.
Russian and Chinese engine options are the best ones.
F-100 is a very big engine compared to RD-93, thus will be a hard job to accommodate it in JF-17s, will need redesign or a bigger air frame required.
F414 is a good option.
Also, in JF-17 airframe, additional space has been left in case a slightly larger engine is to be fitted without any redesigning of the airframe.