In order for the human species to really progress, all human interactions properly need to be ones of mutual benefit - ones where each party is gaining and none are mooching off the productive efforts of others. If an individual determines that s/he will not gain from a proposed interaction then s/he properly does not enter into to it. Whether such net gain will occur is certainly easier to see if the price is set ahead of time and must be paid for before possession of the product can take place or the service begins (although even there for various reasons, after-purchase net gain may vary either up or down from what was beforehand estimated). However, as is very common on the Internet, if s/he samples a service - provided first as a speculative investment by the producer to prospective clients/purchasers/users/etc, and decides that it is not to hir liking sufficient to continue, then s/he properly withdraws from further use. If however s/he decides that s/he does like what s/he has sampled and wants to continue to make use of the service, then a determination of how much s/he values it relative to a medium of exchange is warranted. To continue to use a service without returning value to the producer of it is to take advantage of those who are supporting the producer, sometimes the producer hirself out of hir own assets, or even to eventually cause the service to disappear. The common word for this is to mooch, "to take without giving back" - in other words, to take a product/service that you consider to have value without returning that value, in either a common objective form (money or its equivalent) or in a form valued by the producer of the product or service for as much money or its equivalent as that product/service is valued by you.
Anyone who has use of a computer, even one borrowed, and is therefore using one of the many websites offering services of information/advice has both the ability to make this determination of commensurate value and sufficient funds to pay it. Being on a "fixed income" is no barrier in actuality. It is simply a matter of rating one's priority of values. Is the service (for a month, as an example) or a specific product equal in value to a rented movie? Or the additional cost of a meal eaten out instead of at home? Or an evening at a club with friends? Or a sports game or concert attendance? Or a pack of cigarettes? Or a six-pack of beer? Or an assortment of high calorie snacks? Or some other item which one can choose not to purchase/consume/attend and will not deprive oneself or dependents of necessary food, clothing, shelter or items for basic health maintenance. Very few, if any in the developed world, do not have significant amounts of such "whim" or "fun" money.
Ask yourself how much the service for the past month (or week) has been worth to you compared to some other item of value that you purchase on a regular (or even irregular) basis. Whatever that amount is should properly be what you return to Rob so that mutual benefit has taken place. Maybe you would like to take Rob up on his suggestion to return value to him via a particular type of volunteer effort? By doing so you would then be ensuring that the interaction of his provision of information, and your usage of it, was to mutual benefit. He provided information determined by you to be of value and you provided services that he had stated were of value to him. Mutually beneficial exchanges do not require the exchange of money; they need only be mutually agreed to be of benefit to each.
If you don't think much of the website, then don't continue to use it. If you do value OpEdNews.com, don't be a moocher, be a value trader!