Al-Khalid is actually somewhat expensive at nearly 2.6 mil each after the Ukrainian engine upgrade. This is more due to amortization after replacing the old engines, though. Newbuilt Al-Khalids with Ukrainian engine installed from the start should be cheaper. Al-Khalid is an improved design based on a rejected Chinese tank project known as the Type-90 or MBT-2000, not on the Chinese Type-96. The hulls are very different and a cursory glance at the driver's hatch location should tell you this immediately. Ironically enough, the Chinese themselves are still marketing the MBT-2000 as a direct competitor to Al-Khalid.
Actually, none of the Chinese ZTZ-9x tanks is a direct copy of the Russian T-72. They use many of the same components, but they are mostly self-developed and quite different from the Russian T-72/90 family.
The ZTZ-96 (Type 96) hull is based on the Type-88, which is based on the Type-85, which is based on the Type-59, which is a licensed T-54A. Internally, the arrangement is akin to that of a larger, more heavily armored T-54/55, even retaining the ammo storage space on the right side of the forward hull. The turret is developed straight from the Type-85 III turret which was an indigenous Chinese product. The geometry of the Chinese Type-85 III turret is completely different from that of any modern Russian design and internally resembles more closely the traditional T-54/55 geometry. This ironically means that the inside of these tanks is slightly more spacious than that of the Russian T-72 because the T-54/55 of course fitted THREE people in the turret as opposed to two in the Chinese tanks. The external boxy shape is inspired more by Western than Russian designs - most likely due to US help in the form of the Jaguar project - and the modular armor blocks are possibly a legacy of the pre-2001 military cooperation with Israel. However, the ZTZ-96 still suffers from very thin side armor protection behind the boxy front. The VT-1A variant of the Type-96 was offered to Peru in 2009 (as MBT-2000P) and five examples were delivered but it is not clear whether these tanks will equip Peru's armed forces for real because there is now a dispute with Ukraine over the engine for these tanks. The contract was signed in January 2010, though.
The ZTZ-99/99G/99A1 (original Type 99) hull is fully indigenous despite looking superficially like that of the T-72. Internally and externally, the hull is very different because it is much longer and slightly wider. This is because the original Type-99 variants use a huge German MTU diesel with a separate turbocharger section that is not present in Russian and Ukrainian diesels. The rear of the original Type-99s' hull is enclosed and the exhaust of the engine goes out from the right side of the hull instead of the rear as in the T-72. The turret, as in the Type-96, is internally similar in geometry to that of the T-54/55 but externally boxy like in Western tanks. This results in very thick cast walls in the frontal side sections but very thin sides behind the bend, similar to T-72. With the introduction of the ZTZ-99A2, the hull is now practically the same as that of the T-72 in shape and dimensions although there are still some discernible differences (such as lack of self-entrenching blades and a taller rear section). This is due to adoption of Ukrainian diesel engines (or copies thereof - possibly abetted by Pakistan) that allow the vehicle's hull to be shortened. The most important difference, though, is that the Type-99s weigh between 52-56 metric tons. This is heavier than any Russian tank produced after the T-10. The added weight comes from the wider and longer hull and somewhat larger turret of the tank compared to the T-72 family. It doesn't mean they're "better". They're just less weight-efficient than equivalent Russian tanks. The tanks are also more expensive to produce despite a much larger production run than the T-90 family due to these factors. The Chinese Type-99A2 currently in production cost somewhere between 2.8-3.2 million each if reports are to be believed. No variant of the ZTZ-99 is offered for export, although individual components may be.
Where the Chinese do copy the Russians completely is in the weapons systems of these ZTZ-9x tanks. All of them use 125mm guns with exactly the same autoloader arrangement as in the Russian T-72. However, even in this there are differences. The Chinese coupled their weapons to western-style FCS, including an independent 360-degree TI periscope, earlier than the Russians did and use longer DU sabot rounds derived from their Israeli-designed 105mm APFSDS rounds. However, the risks of ammo detonation inherent in all T-72 family tanks is of course still there.
The Chinese Type-59D is still in production for export customers and it's dirt cheap as you say. Why anyone would want to buy them (even if totally broke) is beyond me. However, there is little doubt that this is the damn cheapest real tank money can buy today. Note that some ex-Warsaw-Pact countries do sell T-72 variants cheaper, but these are taken from old stock, not newbuilds. The real newbuilt T-72 copies and upgrades are usually more expensive.