As a total newbie to this forum, it's nice to have a question I can answer! LOL.
1. We also keep the house very cool (62 day, 57 night - love the programmable thermostat!!!). Your biggest problem will be getting the seeds to germinate; actually growing in cooler temps will result in slower, but sturdier growth, which is good. I pre-sprout things like tomatoes, peppers and eggplant in moistened paper towels, rolled up with the *labeled* seeds inside a plastic baggie and placed in a warm spot, like the top of the refrigerator. After a few days, I begin checking them daily, looking at each seed for emergence of a root tip. As soon as I see this, I remove that seed and transfer it to moist potting soil *carefully* - don't break this little root tip, or it will die. I return the unsprouted seeds to the baggie, cover the planted sprout's container with plastic, and put it in the warm spot with the seeds until the seedling breaks the soil. Now it needs light more than warmth. I have never had luck using a windowsill - the days are still too short this time of year, and with all my houseplants and other things I'm over-wintering inside, window space is at a premium! So I use inexpensive flourescent shoplights. Don't waste your money on grow lights - plain old flourescents are fine, and they don't use much electricity. But the light has to be only a few inches above the plants - any farther, and the light diffuses too much to provide the seedlings with the light they need. I have a setup with some metal shelving, 4' shop lights on a timer (about 14 hours on, 10 off) hung on chains with s-hooks so I can adjust the height of the light fixtures as the plants grow. I also run a fan on the seedings for a little bit each day, or, when I pass them or check on them, I "pet" them - running a hand lightly over them to move them a little. This simulates wind, and results in sturdier, stockier plants. (Sounds crazy, I know, but I swear it works!) Keep them watered but not soggy. Too much warmth and moisture can promote a fungus that will kill them (called "damping off"). But they can't be allowed to completely dry out when they're really little, either. So you need to check them at least daily. I water them from the bottom, pouring water into a dish and letting the pots soak it up from the drainage holes. Let them soak for a little bit, then pour off the excess water so they don't drown. Once the temps outside warm up, you have to start "hardening them off," because these indoor-grown babies are very tender! They aren't used to full sunlight, wind, cold nighttime dew, etc., and they can sunburn, freeze or go into shock (really!) as a result. I begin transitioning them to outdoor life by putting them out on warm days in a mostly shady spot and bringing them back in at night. Gradually (over a period of at least a week or two) move them into sunnier and sunnier areas until they're in full sun, and if nighttime temps permit, leave them out overnight. Now they're ready to go in the garden.
Is all this worth it? For me, yes. I'm itching to start gardening this time of year, and playing with seeds is all I can do with the snow flying outside. Also, I can grow varieties and types of veggies/plants that I can't get at nurseries. (Various rare heirloom tomatoes, interesting hot peppers, pink, white and/or striped eggplants, Oriental veggies, kohlrabi, etc.)
Is it cost-effective? I can likely buy plants cheaper at a nursery, by the time I've included the amortized cost of my shelves and lights, electricity, potting soil, seeds, etc. But in the off-season, I use the shelving for other things, I recycle potting mix and use things like toilet paper rolls and egg cartons to start my seeds in, and I trade for seeds and save seeds from my garden for next year. And I try might selling extra seedlings at some point, which would really help justify it.
2. $1.50/pack. Probably more for strawberries, but I haven't bought them that way, so I don't know. Like PCJ said, bare-root strawberry plants via mail-order will be far less expensive and you'll have a greater selection of varieties to choose from. I've heard good things about Indiana Berry, Krohne Farms, and Norse Farms, but I've not used any of them yet myself. I plan to this year. I wouldn't buy cucumbers, zucchini, squash, watermelon, etc. as plants - they don't transplant very well, and they're easy to start from seed in the garden. Lettuce, peas and beans are easy, too. Tomatoes, peppers, eggplant, broccoli, cauliflower, and brussel sprouts are things that come to mind that are best started indoors early or purchased as plants.
Hope this helps!
Diana, who's going to start a dozen varieties of heirloom tomatoes in the next few days!

But who hasn't ordered any other seeds that I need yet because I can't decide on which varieties I really *need*...
