Alan Yau has opened a cut-price Chinese in Soho. But you should see his brother Gary's place round the corner...

Yikes. Tonight's first finger of sushi just cost the same as my entire lunch. That's a bit scary. It's even weirder when I realise that my tea-smoked chicken with noodle lunch was at Alan Yau's new Cha Cha Moon (cost: £3.50) and this single yellowtail nigiri (cost: £3.50) is at his brother Gary Yau's new restaurant Aaya.

So we have two brothers a few streets away from each other in Soho; one doing cheap Chinese, the other not-so-cheap Japanese. But what am I doing here when I have been doing so well with my self-imposed dining budget of £80 for two? Well, I'm here because Aaya is irresistible. The first time I saw it from the street, I was bowled over by the massive oak door, the fresh orchids in the window, the low-line Italian furniture, the long, light-filled cocktail bar, the shimmering, rippling wall, the staff wandering around in off-the-shoulder dresses or flowing martial-arts harem pants. I stopped in, not to see what sort of food such a celebration of modern design would serve, but to see if they would deign to serve food at all.

I love the regeneration of Soho, what with Quo Vadis, Café Boheme et al getting nipped and tucked, but it's all restoration and nostalgia rather than soaring into the future. British restaurateurs, on the whole, seem very scared of the word modern.

So now I'm dead curious to see whether I can afford enough to eat to keep my body functioning. The sushi here is sublime, but prices go as high as £5 a piece for fatty tuna and sea urchin, so that's out. But maki inside-out rolls are surprisingly good value, with a prawn tempura roll delivering five generous rounds for £6. The rice is blood-warm and lightly vinegared, and the sweet, crisp-coated prawn is benchmark tempura.

Aaya does delicate more easily than it does robust. As a starter, king crab legs (£7.50) are slashed open and topped with a glistening jelly of lemon soy. Flavours tingle like sherbert, both briny and sweet. A classic agedashi dofu (£6.50) is lifted by the creamy nature of the deep-fried tofu and the dried bonito flakes that wave eerily in the heat. It is all classy stuff, but I still need a little more food value.

Waiters are generally helpful and eager, but with few helpful descriptions on the menu, and price being no indication of portion size, ordering can be a bit of a lottery. Does everyone know what constitutes toban yaki, buri daikon and oshinko, and shiso maki – or could you do with a hint?

Kakuni (slow-braised belly pork, £8) and good old chicken teriyaki (£7.50) fill the bill; one a likeable, styled-up Japanese stew with big cubes of wobbly, almost spreadable pork sitting in meaty juices along with vegetables, and the other an artistic array of tender chicken pieces, asparagus, chilli peppers, okra and mushroom scattered over a hoba leaf and splashed with sticky teriyaki sauce. Steamed rice (£2) turns them both into a real meal deal.

But phooey, the wines I want to drink are all over £40, so I have to go Patagonian with a berry/cherry 2007 Valle Perdido pinot noir (£24). Its cachet is at least heightened by the exquisitely fragile Japanese glasses, as fine as light bulbs.

Downstairs is a 10-metre sushi bar and more dining, but at this stage the lively Soho clientele play and stay on the glam ground-floor bar. They are almost universally tall, handsome, well-spoken, beautifully dressed and rolling-in-it bishonen (a Japanese popular culture reference, don't you know, meaning beautiful young men). I say almost universally, because they let me in. But at least I am tall.

With a head chef and three others hand-picked from Kyoto, and a sushi chef direct from Tokyo, Aaya is aiming at London's top bracket of Japanese, undercutting them on price so that I can (just) afford to eat there. But even if I couldn't, I would ask if I could just sit there and admire it.

16/20

Scores: 1-9 stay home and cook, 10-11 needs help, 12 ok, 13 pleasant enough, 14 good, 15 very good, 16 capable of greatness, 17 special, can't wait to go back, 18 highly honourable, 19 unique and memorable, 20 as good as it gets

Aaya, 66-70 Brewer Street, London W1, tel: 020 7319 3888. Lunch and dinner daily. Around £80 for two, including wine and service

Second helpings: More Japanese joys

Nanakusa

441 Sauchiehall Street, Glasgow, tel: 0141 332 6303

David Wan's cool, minimalist, modern grill has a 100-strong menu that runs from sashimi and sushi to yakitori, teriyaki and soup noodles

Mantra

6 The Colonnade, Verulam Road, St Albans, Herts, tel: 01727 811 115

Contemporary Asian cooking combined with Japanese classics for everything from tempura, sushi and ramen to scallops in butter sauce and wagyu steak

Saki

4 West Smithfield, London EC1, tel: 020 7489 7033

Now the fuss over its paperless loos has died down, let's focus on what Saki does best – modern cooking, from crunchy chicken to Iberico pork with miso sauce

Terry's credit-crunch challenge #7: For three months, our critic is eating only at restaurants where the bill does not exceed £80 for two

Read Terry Durack's new column at independent.co.uk/eat