It is not. If you think this is likely to be a major obstacle, consider using your personal resources to meet at least some of this cost. After all, you will be saving money in terms of commuting costs, lunches and work clothes. If you already have a personal computer at home, perhaps you should offer to use that for your work, at least until both parties have given this telecommuting business a try and are happy to continue on with it. As with any negotiation, the best outcome is one with a win-win solution.
Telecommuting has many advantages for employer and employee alike.
But it is not for everyone. If you are not self-disciplined, if you need supervision to keep you on track, then it's not for you. It's probably not best suited for projects that require you to work as part of a team if that means you need to be sitting around a table together for much of the time. But most importantly, telecommuting requires a relationship of trust and goodwill between employer and employee. If your employer doesn't trust you, then you will have an uphill battle getting this thing to fly.