I've recently purchased a new car which requires most of the maintenance work to be carried out from underneath. For this reason I've been looking into trolley jacks. The car is fairly low and to allow for a block of wood to be placed between the jack and jacking point, the jack needs to start from as low a height as possible. Also in order to gain good access to the underside of the car, the jack needs to be able to lift as high as possible. Finally the jack needs to be portable as I will be storing it up about 5 flights of stairs from the garage. I carried out quite a bit of research and found the following options.
By far the easiest to obtain and, especially if purchased second hand, cheapest are steel low entry trolley jacks. This style of jack typically lifts from below 100mm up to a height of around 450mm. Steel trolley jacks weigh in the vicinity of 37kgs. This amount of weight makes the jack extremely difficult to transport. For this reason steel trolley jacks will only suit if they are to be left on the floor, in the garage.
For a lighter weight solution it is possible to get jacks constructed of steel and aluminium, the example I found being the popular Arcan jack typically sold at Costco.
These jacks are highly recommended on line (Costco (Arcan) Trolley Jack - Servicing - Automotive - Whirlpool ..., Arcan-low-profile-trolley-jacks) and can be had for around $170. I purchased one of these jacks to use myself however, I soon found that the jack, at 26kg, was still too heavy for my requirements. The Arcan jacks are suitable if they will need to be transported rarely in a ute or similar but for regular relocation they are still too heavy. Given the price and the weight, these are my choice of trolley jack if transportability isn't a consideration.
The next step in lightweight jacks is to source one constructed wholly of aluminium, this is where it starts to get difficult. There are two known brand names that supply two different styles of aluminium jacks, they are Kincrome and Armstrong. The Armstrong jack is priced at $500, too expensive in my books.
The Kincrome jack can be found on line for ~$350.
The benefit of both of these jacks is their weight, a mere ~13kg. This is incredibly light and makes them very attractive. What's more, a bit of searching on eBay reveals that Chinese copies of both of these styles of jack can be found for as little as $225 with the average being around $300. Where these jacks fall short is in the maximum lifting height, ~10cm lower than the two previously mentioned jacks, and their lifting capacity of ~1000kg. The lifting capacity isn't as issue for me but the lifting height definitely is as I've used jacks that only lift to approximately this height before and it can be quite annoying getting the car on jack stands, especially at a reasonable height. Furthermore some searching revealed that the reliability of these jacks isn't great (Kincrome 1000kg Trolley Jack - Servicing - Automotive - Whirlpool ...). Also evident from the above link is a possible lack of warranty support from the brand name versions. Still, buying one of these jacks for ~350 with a warranty from Kincrome seemed like the best deal. Until I was directed towards Joplin jacks.
These jacks (website no longer exists) are similar in design and dimensions to the Arcan jack mentioned previously meaning the lifting range is essentially the same however, they are made wholly from aluminium so are 8kg lighter (18kg). These jacks are hard to find information on, probably due to the fact that they are Australian designed and certified (made in China for Joplin) however, they come with a 1 year manufacturer warranty which is as good as any of the previously mentioned jacks. I know a couple of people who have been using these jacks for 5 years or more and have never had a problem with them. As you can see on the website these jacks retail for $400 which is getting quite expensive but even at that price I believe they are value for money given their lifting range and weight.