If you have not already done so, I suggest you search the amplifier forum for information on "vintage" gear, including Marantz.
I have purchased off eBay and now own a number of 70s era Marantz components including two 2235B receivers, a 1070 integrated amplifier, and a model 125 tuner.
I had both of the receivers checked and cleaned, and the FM tuner I.F. stages aligned by a competent repair shop, and at the same time they also replaced any burned out bulbs.
The 1070 amplifier has not needed any repairs, nor the 125 tuner (this tuner was aligned for me by the seller, who was a Marantz technician for many years).
These Marantz components were built using the highest quality parts and care during assembly. While individual units may have developed problems requiring a trip to the repair shop, in my experience these are the exception. Maybe I am just lucky, or a good judge of a good deal vs. one that is too good to be true, but my eBay purchases have all been solid values.
The most common parts failure on the vintage Marantz gear is the power switch, but suitable replacement switches are available so this is not a worry.
I did purchase one 2220B receiver for $20, but I knew I was buying a parts unit, and really just wanted to take off the feet and the knobs to replace ones that were missing or damaged from one of my 2235B receivers. This unit was smoke damaged, and reeked so badly I did not even want it in my home one minute longer than necessary, but as a parts unit it was a good deal.
If the unit is being sold on eBay, try and buy one from the original owner, from a smoke-free home. Smoke damage is one form of hidden damage to older audio gear.
Next, try and buy gear from one of the dryer, cooler climes rather than the gulf coast states or Florida, because in warm humid climate, even a short period of storage in an unairconditioned shed or garage can cause corrosion in no time at all.
Finally, when you have made a purchase of one of these fine units, pay a bit more to ensure that the seller does a first rate job of packing the item for shipping. This means lots of bubble wrap and packing peanuts, and double boxing the receiver for shipping.
A good deal would be a clean working Marantz receiver such as a model 2215 ,2220, 2220B, 2225, 2226, 2230, or 2235 for anthing close to $75-$100. For that price, the unit should be working flawlessly, perhaps with a few bulbs needing replacement. One with the optional and expensive walnut case will usually cost more. In the integrated amplifiers, the 1060 and 1060B are very common and usually sells for around $80, but I like the size, look, feel and features of the Marantz model 1040, 1070, and 1090 integrated amplifiers.
A properly working vintage Marantz receiver, even one of the lower powered units, will outperform any modern solid state headphone amplifier costing less than $400, and perform as well or better than many costing much more.
I regularly scan the eBay listings of Marantz gear, when I see a particularly good deal I try and post on the amplifier forum to let people know.
The last really good eBay deal I saw, and passed on because I already have too much stuff, was for a working Marantz 2010 receiver (actually a somewhat rare model) that was very clean except that it had a spliced power cord and needed to have the tuner dial pointer restrung, offered with a Buy-It-Now price of $35. This auction did not last long before someone bought it.