Both Home Depot and lowes have garden top soil on sale 50% off usually at the beginning of each season. That might be a good start. Also get some compost.

I have never been impressed with the bagged topsoil or compost from the big box stores. Read the ingredients panel (on the back, near the bottom, usually) and see what "may" be included; pretty vague. There are some brands carried by nurseries that are better. I checked out a bag of commercial "raised bed mix" today and found it "may contain" topsoil, composted manure, peat moss, coir, etc. All these are fine, but by the soft feel of the contents and light weight of the bag, I suspect there's a good deal of peat moss in there. Peat moss is not a great amendment for the garden for several reasons, which I won't delve into here.

Loose topsoil, compost, or mushroom compost from a reputable nursery is great, if you have a way to transport it, or need enough to warrant delivery, which you will pay for.

You can always mix up your own if you have home-made compost and topsoil.

Roses and perennials are a long-term investment - they take a while to get established - usually three years to really get going ("first year they sleep, second they creep, third they leap" is the old saying) so it is worth the effort to prepare the bed well the first time around. Annuals are just here for the one season, so if you don't get it right the first season, you can always fix it the next.

We have a local sand and gravel type place that will deliver nice top soil, and even compost by the cubic yard. It is cheaper than by the bag, if you can pick it up say in a truck but delivery is a flat $100

Mushroom soil is best, particularly for vegetables. I would not buy soil from big box stores. You would do a lot better if you go to a nearby nursery and have them deliver a couple of yards for you.

I agree that the big box stores do not have good soil. I get Fafards potting soil from Coppolas, I would check there for top soil, if you are close. They are a little pricey. http://www.coppolasgardencenter.com/ They are a family business, been there many years.