Take risk, break the rules, use low tunnels and row covers. plant more than you think you can sell. plant again a week later. it won't always work cause mother nature is in control. This year in my area it worked out. Next year??????

There are lots of ways to start plants early. Jnj mentioned a few but you could just start many plants early in your house using lights. To really push the season with warmer weather crops a tunnel or greenhouse is better. I use a combination of many things but sometimes earliest of plantings don't pan out. Certain crops like onions, peas, spinach and other greens can be planted out early and will produce a marketable crop in 40 to 60 days. Many other warm season crops can be aided by a combination of black plastic mulch for planting through to warm roots and a row cover overhead to keep foliage warm. As you might guess these technologies require purchase of materials (cost), and take extra time to manage.

I agree with jnj, take risks. At first I started planting 5 seeds out of a packet of 25 seeds because 'I needed to save some for next year' lol. A couple months later at harvest time, I realize 3-5 plants is NOT ENOUGH! Now I'm sowing every seed I can get my dirty hands ON. I stay away from electrical lights to grow things which means sticking to whats in season. If necessary, check out ancient methods for extending crop seasons using things like warm clay bricks beside plants etc. Also try new methods like Bill Mollison's 'imitating the forest floor' or Ruth Stout.

Edit: I've been fortunate enough to get nearly 100% germination rate for the past 3seasons ordering from Baker Creek Heirloom (I wish they would pay me for every time I mention them).