I have had a couple of failures of handheld insulation testers over a 30 year career, but they are quite rare. A Megger BM223 failed, a DiLog DL9307 popped the varistors and I have just had a MetraHit unit fail. Personally, I wouldn't get too dismissive of handheld devices, especially if you have a limited budget.
I have had a UT513 for coming on 20 years now and it still works fine, it is likely that the design between the 511 and 513 will be very similar, and build quality should also not change. There has been revisions to the unit since mine was built, so you cannot really use these older units as a guide.
They do use size C batteries, which isn't one that I have around a lot. It makes the units a little bit heavier, but on the plus side they last for ages. My UT513 will also operate whilst still plugged into the mains adapter. There is no tilt stand on these units, so if you are using it for a lot of bench work, the viewing angle is not always the best, it is either stood up straight or laid flat. You can of course build a stand for it or prop it up. Out in the field I do not find this an issue. You also have to swap over connections between measuring resistance and voltage.
Generally insulation testers above 1kV do not have a resistance range as the apparatus that you are testing with them, will have very low resistances and a micro-ohmmeter is used to test these that is 4 wire test and higher current for improved accuracy under these circumstances.
I would suggest that if you are purchasing a 5 kV insulation tester for destruction testing, you are likely to be quite disappointed. The insulation testers are designed to push out 1mA max at full voltage, after that the voltage will drop off rapidly and the short circuit current will be under a couple of mA. This limits the energy output, and it just isn't enough to cause any serious destruction. There are exceptions to this of course if the apparatus under test is rated for very low voltage and the test voltage is massively excessive in comparison, then you may get a few sparks.
There are a number of devices out there in your budget range, it just depends what you are testing and the kind of results you want. Are you actually going to use DAR and PI functionality or are you just quick insulation tests for verification?
What kind of insulation resistance values do you want to measure up to? The manufacturers often quote the max insulation reading for the 1kV range, at 500V test voltage and below, this is often less, you need to look at the actual data sheet to get a better idea.
The Extech instruments are quite cheap, but are usually CEM rebrands and the build quality I have found to be a bit of a cross-fingers affair. There are some Mastech units out there that may be of interest to you, but are also cloned quite a bit and offered cheaper. The cheapest insulation tester I have found is a VC60B+ derivative units that are actually not that bad given the price tag, may do you just for intermittent hobbyist use.
Basic insulation testers aren't usually that complex, is there anyone close to you who could assist with fault finding on the Megger?
Most of my insulation tester reviews are on element14, and I haven't really started looking at the cheaper units yet.