Nothing that is immediately suitable. If the charger module in the car were designed to be bidirectional (rather than just AC->battery as it is at present), then it would be more expensive. There would also be significant safety complications in making the AC bidirectional, wheras the DC connection is inherently bidirectional.
So if you look at the price of a solar inverter, add a substantial extra cost for the CHAdeMO or CCS protocol controller, contactors and connector (the CHAdeMO connectors in particular are not cheap), you get the notional price of one of these units. Add then an allowance for the fact that these are currently only built in low volumes and you get the price you see now (actually, £8k-£9k is a pretty good price as things stand today).
Personally, I'm not at all convinced that full V2G is a good idea. You can get most of the benefit with very much smaller cost by simply managing EV charging speeds/times. In such a scheme, you would input by some mechanism the amount of charge you need and when, and the system would charge at time and rate to suit grid balance - maybe not charging at all some nights when you have enough for your commute the next day, maybe charging more than you need on other nights when there happens to be excess. This also side-steps issues of battery wear, and accounting for losses in the charge/discharge cycle (if you do real V2G, you are getting less out of the battery than you put in and need to account for that in the billing).
