It depends on application, which you haven't specified really. Is this a smaller hobby machine or a larger commercial machine? If the latter, there is no way around the fact that the drives and motors are going to cost a lot unless you find a deal on some used equipment. If it's hobby, then they are available but still a bit of a premium. However, if you are buying an IP-A, then you probably aren't an average hobbyist in that case anyways. I can't speak to how good they are, etc. but here's a servo drive that works with DC servos and operates on analog inputs. It also provides encoder feedback to the controller via the DB-9 connector, so both the drive and the controller/Mach are getting encoder information. This is a smaller drive, but if you don't need a lot of power then I believe they would work with the IP-A and don't cost quite a fortune at around $500/ea (though if you are comparing to Geckos or other drives along those lines, it does seem like a lot more).
http://www.applied-motion.com/products/servo-drives/sv7-q-afFrom what I've read in the manuals, the "AF" version is the one with encoder feedback specifically for analog applications, though others also work on analog signals without the more convenient encoder integration. I suppose that one advantage of these drives is the motors would be relatively inexpensive as well, but I suspect that you'd be in for around $2200-2500 for a complete 3 axis system including power supply, servo drives, servo motors and encoders. I also found at least a half a dozen other vendors of similar drives, though these were some of the better priced models and are sold/backed through a U.S. based company (though made in China by the looks of the markings). There are cheaper from likely less reliable distributors, and also more expensive. I just googled "DC Servo Drive Analog Inputs" and found the best way to find what is available to look at the "Images" results in google instead of the web results.
A couple other results (again, mostly hobby sized since there is no problem finding expensive commercial products with analog inputs):
http://www.motioncontrolproducts.com/drives/DSD806-digital-servo-drive.phphttp://www.zappautomation.co.uk/en/jd-range/518-jd430-aa-000-ac-servo-driver.html (this one is getting to the more commercial/industrial side)
http://www.midwestmotion.com/amplifiers.htm