I recently purchased a RAM-modified Oppo 981. It is far, far beyond my expectations. Amazingly so. Before that I modded a few components of my own. This gave me a good basis for evaluating different modders claims. It is daunting ordering something like this without audition, but if you take the time to really understand what they are doing then there really is not that much risk.
Number one is you need to upgrade internal power supplies. These make a huge difference, as you can easily prove to yourself. Just get some high speed soft recovery HEXFRED type diodes and solder them in for the cheap diodes in your amp/preamp/cd player/whatever. Trust me, they will be cheap diodes in there. Then, when you hear how much better just that one tiny change sounds maybe you will begin to understand how something like a little RAM modded Oppo 981 can give an Esoteric DV50 a run for its money. Or even beat it, depending on the listener, it is that close. Because RAM goes way beyond this simple mod, using hard wired surface mount diodes and Jensen 4-pole caps. (I'm talking only about the power supply right now.)
Then you look at things like the clock. Google around, no problem finding lots of reviews of top-end players improved by adding the Superclock 2, 3 or 4. In doing my research I found several reviews saying if you have Superclock 2 (or 3) it is worth upgrading to Superclock 3 (or 4) they are that much better. And the clock in turn was much better than stock. That one also is a no-brainer. And yes for the Esoteric as well as the Oppo. Superclock improves them all.
Something like replacing output stages with different op-amps, you have to trust the modder a little. But even here it should be easy to see where there is room for improvement, as far too many of these spendy players use way too complicated circuit design. Simpler is better is the rule of the day. I've talked to Kyle and Doug at RAM, a lot of what they do is throw out overly complicated and unnecessary circuitry and replace with simpler, direct-wired parts.
Another thing you might try, replace some caps with higher quality same value caps. Amazing. Most of these modders replace a handful of caps, this is a fool-proof guaranteed path to improved sound.
I should also note there is no conflict whatsoever in all modders claiming their mod makes the player competitive with players costing 3-4X. They could easily all be right. Now if they claimed their player sounds better than any other mod, thems would be fightin' words. But they don't. Of course when done with the $250 Oppo you really have a $1465 player, but even then I think it is quite fair to say it is better than players costing 3 or 4 times more, ie $4500 to $6k. In fact based on my experience I would say that claim is quite conservative.
As for how much it costs vs what you get, depends on what you started out with. Different players with different hardware and design topologies naturally lend themselves to modification to different degrees. Its easy to see how a player with a good transport mechanism and DAC, for example, will be easier to mod to a certain level than one with worse trans and DAC, because its easier to improve caps and power supplies than more expensive and hard to install parts like a transport mechanism. And on down the line.
Still, I think you will find (and I know it is somewhere here on Audiogon) people with these incredibly expensive decks who have spent thousands having them modded and will tell you it is some of the best money they have ever spent. I didn't spend that much but I'm extremely pleased with mine.
This all makes sense in consideration of the economics of designing, producing, distributing and marketing a new component. For every $1k you spend maybe $.1k goes to parts. Mod your component and about $.7k goes to better parts. Again, if you try the simple parts swaps experiments I've suggested you will really begin to understand how powerful are the forces working in your favor when you decide to mod what you have instead of buying againg. And again. And again . . .
Frankly, if it was me, and if I was looking at the kind of budget you seem to have, I would be talking to RAM about what deck would be the best starting point for all-out performance. Have them stick in a couple Silver Rocks, mod it to the max. You will have music like you never heard before.