You definitely don't need an architect! You can get ideas of pricing online from the timber garage places. All the attractive timber outbuilding places have good websites, so search and read like mad.
Look especially for examples of previous jobs they've done, particularly if those are priced up on their websites.
Be very careful of how the pricing is quoted - no two companies quote in the same way, some include VAT in pricing, others don't, some quote on a super basic spec and let you add improving options, others start off with a more flash spec and therefore a higher starting price.
The cost of the timber 'shells' looks like amazing value for money at first, but they are normally quoted without decent windows and with a super basic spec roof and no lining or insulation. They will also need a concrete floor and a couple of courses of bricks around the boundary to bolt down onto.
Regardless, don't forget that the quotes you'll get will not include a concrete pad (which will cost more than you'd like!) and a driveway. This will add a good 20% to 30% extra to the cost of the building. Also think about adding power, again the cost can be startling. I suspect by the time you've added double glazed windows, your upper storey, and lining and insulation, decent roofing materials (as opposed to the cheap felt that is normally in the standard spec) you'll be suffering so much sticker shock that the solar panels might not look quite so tempting, sorry to say.
If you don't want to go with timber, breeze block rendered will be a similar price, but may result in damp issues within the garage unless it's very well ventilated (ie, freezing in winter, so not really suitable for DC use in the floor above).
You can do 80% of the info gathering online but nothing beats having a stroll around garage 'showrooms' and having a natter to the proprietors.
If you do decide to go with timber, an ex-showroom garage can give you a great saving if the size & spec suit you, so it's worth looking out for those.
Good luck - this is not a cheap exercise so ideally gather info gradually and give ideas time to percolate.