LHD & RHD differences
Speaking as both an Oz citizen and long term MB owner, I would not consider the conversion from LHD to RHD. I use MB North America service manuals and it is amazing the differences between LHD and RHD cars. Many things under the bonnet (get used to that, its what we call a hood here) except the engine and items directly attached to it are mirror reversed (eg. brake master cylinder/booster, battery, fuse box, wiring harness, ECU and other electronics, steering box and hydraulic lines. Some models require different exhaust manifolds (and engine pipes), and bell housing (with reversed starter motor location). The steering geometry settings are often different. Headlight lenses are different. Inside the cabin there is the steering column, pedals (incl parking brake), instruments, dashboard, control stalks, wiring harness, etc.
Then there are all the issues with Australian design rules (ADRs) and local roadworthy and registration requirements. Oz cars must meet certain emission requirements and have anti-intrusion bars in doors and glass complying with ADRs etc. The list goes on. There are a few grey imports here. They are usually easy to spot. Most are from RHD countries but a small number are converted (often poorly and not completely). They are often problem cars and even if they are not rusty they can be difficult to get through registration and roadworthy inspections. They attract very low resale prices here.
The W124 is considered a "buyers" car here at present. Their prices have dropped in recent times and they are good buying. Yes they will seem expensive compared to other markets but remember they were very expensive here new and our climate is very kind to cars. A rusty W124 (or W126, W201, or newer) is almost unheard of here. Despite being a large country (similar in size to the US) most cars here cover around 15,000km annually (most people work close to home and only travel long distances when holidaying). Mercedes often travel even less. Our 1990 300TE is typical at around 175,000km and my 1990 190E is high at 215,000km.
As a price guide for W124s, talking in Australian dollars, $10,000 buys an early 230E or high kilometre early 300E. $15,000 gets you into good early 300E or a 230TE or late 230E. $20,000 buys update (post 1989) 300Es. $25,000 and you're talking 220E, E220, E220T, 300TE, 300E-24 or low km update 300E and early 300CE. $30 - 40k gets into the late multi-valves (300CE-24, E280, E280T, 320E, E320). Over $40k and your talking 320CE and E320C.
The W124 was popular here and you should have no trouble finding a good one. We have MB clubs here based in the capital city in each state that you may also find helpful.
I hope your move down under goes well and good luck finding a nice Mercedes-Benz.
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.